GOOD  CONCRETE 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


GIFT 


Good  Concrete 


A  Manual 

For  The  Rational  Use  of 
'Portland  Cement 


Riverside  Portland  Cement  Company 

Los  Angeles 

1914 


Copyrighted   1914 

by 

Riverside  Portland  Cement  Co. 
Los  Angeles,  Cal. 


Printed  by 
De  Wit  &  Company 
Los  Angeles.  Cal. 


Engineering 
Library 

TA 


PREFACE. 

In  Portland  Cement  -  Concrete  the  world  has  an  ideal  structural 
material  whose  possibilities  are  limited  only  by  the  skill  and  ingenuity 
of  the  user.  Its  widespread  and  ever  increasing  use  is  exerting  a 
profound  influence  in  making  our  cities  and  towns  safer  and  more 
sanitary. 

The  fire  risk  has  by  its  use  already  been  reduced  enormously, 
and  millions  of  dollars  are  being  saved  annually  in  insurance. 

It  is  doing  much  to  beautify  our  cities  by  the  ease  with  which  it 
lends  itself  to  the  artistic  treatment  of  our  homes,  business  buildings, 
sidewalks  and  streets. 

It  has  given  to  building  operations  an  air  of  permanence  which 
heretofore  they  did  not  possess. 

Once  properly  built  a  concrete  structure  becomes  a  thing  of  per- 
manence. It  will  not  deteriorate  with  age,  it  becomes,  so  to  speak,  a 
part  of  the  geology. 

There  are  few  structural  operations  to  which  concrete  in  some 
form  cannot  be  economically  applied. 

Portland  cement  is  sometimes  abused.  The  seeming  simplicity 
with  which  it  can  be  worked  has  often  led  the  uninitiated  to  attempt 
its  use  without  regard  to  the  laws  that  govern  its  proper  use. 

This  hand-book  is  written  to  present  to  the  cement-user  in  con- 
cise form  the  general  and  detailed  operations  necessary  for  the  full 
realization  of  the  value  of  Portland  cement  as  a  material  of  con- 
struction. 


Contents 


Concrete   Axioms    

CHAPTER  I. 


Portland   Cement    

CHAPTER  II. 


Concrete. 


CHAPTER  III. 

Proportioning   Concrete 37 

CHAPTER  IV. 

The   Properties  of  Concrete 53 

CHAPTER  V. 
Portland  Cement  Sidewalks    73 

CHAPTER  VI. 

Portland  Cement  Curbs  and  Gutters 101 

CHAPTER  VII. 

Concrete   Roads    HI 

CHAPTER  VIII. 
Specifications  for  Concrete  Roads  with  Asphalt  Oil  Wearing  Surface 123 

CHAPTER  IX. 

Cement    Pipe    151 

CHAPTER  X. 

Cement  Sewer  Pipe   1 65 

CHAPTER  XI. 

Some  Suggestions  for  Care  and  Return  of  Empty  Sacks 171 

Appendix 1 79 


CONCRETE  AXIOMS. 

Concrete  construction  does  not  belong  to  the  class  of  iDork  that 
can  be  done  by  unskilled  labor. 

Definite  laws  govern  the  use  of  concrete  as  well  as  all  other  struc- 
tural materials. 

Good  rock,  sand  and  cement  will  not  make  good  concrete  in  the 
hands  of  inexperienced  workmen. 

Don't  guess  at  proportions — measure  them. 

The  cement  in  a  concrete  is  the  smallest  of  its  ingredients.  Don't 
make  it  smaller  than  the  specifications  require. 

Cement  is  the  only  ingredient  in  a  concrete  or  mortar  that  has 
been  scientifically  and  accurately  made.  It  is  a  finished  product 
as  it  comes  on  the  market,  in  the  preparation  of  which  great  care 
and  pains  have  been  exercised,  whereas  the  sand  and  rock,  which 
constitute  more  than  80%  of  the  total,  are  natural  products  and 
have  been  collected  at  random. 

Use  clean  materials.  Cement  cannot  bind  sand  and  rock  to- 
gether if  clay  coats  them. 

Concrete  cannot  be  any  stronger  than  its  weakest  ingredient.  There- 
fore, use  sand  and  rock  whose  individual  strength  is  sufficient  for 
the  purpose. 

Don't  use  very  fine  sands,  or  those  containing  much  quicksand. 

Test  all  your  materials  for  strength  and  fitness  for  the  purpose  to 
which  they  are  to  be  put. 

Cement  needs  water  to  properly  harden.  If  it  is  robbed  of  any  of 
the  necessary  water  its  strength  suffers.  Too  much  water  is  as  bad 
as  too  little.  Learn  to  use  the  right  amount. 


Protect  fresh  concrete  from  drying  out. 

Don't  lay  concrete  in  cold  weather.  Cold  retards  and  warmth 
hastens  the  hardening  of  a  concrete  or  mortar. 

Don't  blame  cement  for  poor  work  before  you  have  considered 
every  factor  that  might  have  contributed  to  the  failure.  Men  and 
materials  are  just  as  liable  to  be  wrong,  and  more  so,  than  the 
cement. 


Portland  Cement 


CHAPTER  I. 


The  term  "Portland"  as  applied  to  cements  is  used  to  distinguish 
the  superior  artificial  hydraulic  cements  from  the  inferior  natural  ones. 

Portland  Cement  is  not  so-called  because  it  was  first  made  in    What  is 
Portland,  Ore.,  or  Portland,  Me.,  but  to  the  fact  that  in  1824  when    Portland 
John  Aspden  made  his  first  artificial  cement,  its  color  resembled  the    Cement? 
Portland  stone  much  used  at  that  time  in  England   for  masonry. 
The  definition  of  Portland  Cement  will  be  found  under  the  "Standard 
Specifications"  of  the  Am.  So.  C.  E.  given  below. 

STANDARD  SPECIFICATIONS  FOR  PORTLAND  CEMENT. 
AMERICAN  SOCIETY  FOR  TESTING  MATERIALS. 

The  term  "Portland  Cement"  is  applied  to  the  finely  pulverized    Definition 
product  resulting  from  the  calcination  to  incipient  fusion  of  an  inti- 
mate mixture  of  properly  proportioned  argillaceous  and  calcareous 
materials,  and  to  which  no  addition  greater  than  3%  has  been  made 
subsequent  to  calcination. 

The  specific  gravity  of  the  cement  shall  not  be  less  than  3. 10  on  a    Specific 
sample  ignited  at  low  red  heat.  gravity 

It  shall  leave  by  weight  a  residue  of  not  more  than  8%   on  a    Fineness 
No.  100,  and  not  more  than  25%  on  a  No.  200  sieve. 

It  shall  not  develop  initial  set  in  less  than  thirty  minutes,  and  must    Time  of 
develop  hard  set  in  not  less  than  one  hour,  nor  more  than  ten  hours,     setting 


12 GOOD  CONCRETE 

Tensile       The    minimum    requirements    for    tensile    strength    for    standard 
strength  briquettes  shall  be  as  follows: 

NEAT  CEMENT 

1    day  in  moist  air 1  75   Ibs. 

7  days  (1  day  in  moist  air,  6  days  in  water)...  500  Ibs. 
28  days  (1  day  in  moist  air,  27  days  in  water)...  600  Ibs. 
One  Part  Cement,  Three  Parts  Standard  Sand. 

7  days  (1  day  in  air,  6  days  in  water) 200  Ibs. 

28  days  (1  day  in  air,  27  days  in  water) 275  Ibs. 

Constancy        A  neat  cement  pat  24  hours  old  exposed  to  steam  over  boiling 
of  volume   water  in  a  loosely  closed  vessel  must  not  check,  warp  or  disintegrate. 

A  pat  24  hours  old  placed  in  water  at  70  deg.  F.  for  27  days 
must  remain  sound. 

A  pat  left  28  days  in  air  must  remain  sound. 

Sulphuric  add       The   cement   must  not  contain   more   than    1.75%    of   sulphuric 
and  magnesia   anhydride  and  must  not  contain  more  than  4%  magnesia. 

We  will  now  consider  the  various  items  of  the  standard  specifica- 
tions, their  meaning  and  use  in  judging  a  cement. 

Specific  By  this  term  is  meant  the  ratio  between  a  given  volume  of  the 
gravity  substance  (cement)  and  an  equal  volume  of  pure  water.  In  short, 
when  we  say  a  cement  has  a  "Specific  Gravity"  of  3.12,  we  mean 
that  a  given  volume  of  it  (solid)  is  3.12  times  heavier  than  an 
equal  volume  of  water.  The  specific  gravity  of  Portland  Cement 
is  higher  than  that  of  natural  cements,  due  to  the  high  degree  of 
heat  used  in  burning  the  former. 

This  test  is  used  to  determine  whether  or  not  the  cement  has  been 
5*   properly  burned.     The  specific  gravity  of  a  cement  is  lowered  by  long 
storage  due  to  the  absorption  of  water  from  the  air.     For  this  reason 
it  is  necessary  to  thoroughly  dry  the  sample  before  it  is  tested. 

This  test  is  made  to  determine  how  fine  the  cement  is  ground. 
The  test  is  made  with  the  200-mesh  (40,000  holes  per  square  in.), 


GOOD  CONCRETE 15 

and  the  100-mesh  (10,000  holes  per  sq.  in.)  sieves.  It  is  essential 
that  the  sieve  be  standardized,  otherwise  the  results  of  the  tests  will 
be  of  no  value. 

When  Portland  Cement  is  mixed  with  the  proper  amount  of  water.  Setting 
a  plastic  paste  is  produced,  which,  after  a  few  hours,  hardens  to  a  time 
stone-like  mass.      The  time  taken  to  produce  this  result  is  termed  the 
"setting    time."      The    setting   time   is    divided    into    two    arbitrary 
periods,  i.  e.,  the  initial  and  final  setting  time. 

Initial  set  is  that  point  in  the  stiffening  of  the  cement  paste  where  Initial 
it  will   bear   a  needle    1/12"   in   diameter   and   weighing    1/4   Ib.    set 
This  point  can  be  approximately  determined  by  observing  the  point 
at  which  the  test  piece  will  bear  slight  pressure  with  the  thumb  nail. 

Final  set  is  attained  when  it  will  support  a  needle  1/24"  in  diam-  Final 
eter  weighing  1   Ib.     Final  set  is  completed  approximately  when  the  $ef 
test  piece  will  take  strong  pressure  with  the  thumb  nail. 

Mix  up  about  4  oz.  of  cement  with  1  /5  its  weight  of  water,  work  field  test 
with  a  trowel  for  five  minutes  until  a  smooth  paste  is  obtained,  roll  /Or  setting 
into  a  ball  and  place  on  a  clean  piece  of  glass  V  X  A",  flatten  out  time 
into  a  circular  pat  and  taper  to  a  feather  edge  toward  the  circum- 
ference.     Place  in  a  cigar  box  lined  with  wet  blotting  paper  and 
try  every  ten  minutes  as  directed  above. 

Riverside  Portland  Cement  will  get  its  initial  set  in  from  1  J/£  to 
2'/2  hrs.,  the  final  in  from  3  to  5  hrs.,  depending  on  the  temperature 
of  the  air.  It  will  be  faster  when  warm  and  slower  when  cold. 

This  test  is  very  important  to  the  proper  handling  of  the  cement.  Use  of  test 
On  it  depends  the  size  of  the  batch  of  mortar  or  concrete  that  can 
be  safely  worked  up  and  used  before  it  takes  its  initial  set.  A  batch 
of  concrete  that  has  begun  to  set  should  not  be  used.  If  the  set  is 
disturbed,  the  strength  is  greatly  reduced.  The  practice  of  adding 
more  water  and  retempering  the  partially  set  concrete  is  one  that 
cannot  be  condemned  too  strongly. 


14  _  GOOD  CONCRETE 

Tensile  Although  cement  is  never  used  to  take  a  tensile  strain,  the  tensile 
strength  strength  gives  a  convenient  method  of  comparing  different  lots  of 
cement  and  noting  the  progress  of  hardening.  The  strength  is  usually 
measured  at  the  end  of  1  ,  7  and  28  days  for  the  neat  and  at  7  and 
28  days  for  the  1  :3  sands.  The  logical  test  would  be  to  determine 
the  compressive  strength,  but  this  procedure  is  both  tedious  and 
more  expensive  than  the  tensile  test. 

Constancy       T  m's  test  js  commonly  known  as  the  "Boiling  Test"  and  is  made 
of  volume  to  determine  the  absence  or  presence  of  any  dangerous  expansion  in 
the  cement. 


7^  determination  of  this  item  serves  as  an  index  to  the  amount 

anhydride  of  gypsum  that  has  been  used  as  a  retarder. 

Generally:  Aside  from  ^  setting  time  tegt)  ^  testjng  of  cement  Js  ft  technj_ 
cal  matter  that  should  be  entrusted  only  to  persons  expert  in  this 
branch  and  who  have  the  proper  laboratory  equipment  for  carrying 
out  the  work.  The  conditions  under  which  the  tests  are  made  must 
be  kept  uniform  in  order  to  get  results  that  will  not  be  misleading. 

HARDENING. 

The  "set"  of  cement  must  not  be  confused  with  its  hardening. 

Between  Setting  is  a  purely  arbitrary  period,  as  has  already  been  explained. 

set    ai  d  The  hardening  of  a  cement,  however,  is  a  definite  chemical  stage, 

'*  and  begins  after  set  has  taken  place.     Hardening  takes  place  either 

in  water  or  in  a'ir—  in  fact,  the  process  takes  place  more  uniformly 

under  water  than  in  air.     The  hardening  is  due  in  part  to  a  process 

of  crystallization,  which  takes  place  in  certain  of  the  elements  of 

the  cement. 

hardline  •  *"  ™T  °f  ^  IatCSt  researches  on  Ac  hardening  of  a  cement,  it 
is  established  that  the  process  is  not  really  as  simple  as  crystallization 
itself.  Michaelis,  Sr.,  attributes  the  hardening  of  a  cement  to  the 
formation  of  a  mineral  glue,  which  is  termed  the  hydrogel,  and  to  the 
formation  of  minute  crystals  of  the  hydro-aluminate  of  lime.  The 
hydrogel  is  composed  of  a  combination  of  hydro-silicic  acid  and 


GOOD  CONCRETE 15 

lime;  that  is,  hydro-silicate  of  lime.  No  definite  chemical  com- 
pound is,  however,  formed,  as  the  composition  of  this  lime  hydrogel 
is  constantly  undergoing  changes  by  the  adsorption  of  lime.  Now, 
the  formation  of  this  mineral  glue,  or  hydrogel,  is  controlled  by  two 
factors — first,  the  temperature;  second,  concentration,  or  the  relative 
amount  of  water  present  to  the  amount  of  available  lime  in  the 
cement.  The  formation  of  this  hydrogel  is  greatly  facilitated  by  agi- 
tation (mixing).  The  critical  temperature  below  which  the  hydrogel 
will  not  form  has  been  found  by  Michaelis  to  be  40  deg.  F.  This 
limiting  temperature  is,  however,  theoretic.  For  practical  operations 
a  minimum  temperature  of  55  deg.  is  the  limit  beyond  which  the 
proper  hardening  cannot  take  place  without  the  application  of  arti- 
fical  heat.  At  temperatures  lower  than  55  deg.  F.  the  "gel"  forms 
but  imperfectly,  and  the  mass  is  more  likely  to  crystallize  in  inferior 
flat  forms,  which  do  not  allow  the  hardening  to  progress  to  the  best 
advantage. 

When  a  cement  hardens  by  crystallization  alone,  it  can  attain  a  Crystallization 
fair  degree  of  strength  if  kept  in  air,  but  such  a  hardened  cement 
or  mortar  would  soon  disintegrate  when  placed  under  water,  owing 
to  the  relative  solubility  of  the  crystals.  Again,  if  too  much  water 
is  used  in  gauging  a  mortar  or  concrete,  the  cement  is  decomposed 
into  "laitance"  (cement  milk).  This  laitance  does  not  set  up,  but 
dries  out  to  a  soap-like  mass  devoid  of  any  strength. 


CHAPTER  II. 


CONCRETE. 

Concrete  may  be  defined  as  a  skeleton  of  rock  bound  together  by  Definition 
a  sand  and  cement  mortar.  It  may  with  propriety  be  considered  of  concrete 
uncoursed  rubble  masonry  in  which  the  stone  ranges  from  J/4"  up  to 
•3",  the  whole  consolidated  into  a  monolithic  mass  by  the  binding 
mortar  setting  up.  The  advantages  of  concrete  over  coursed 
masonry  lie  in  its  adaptability  to  any  form  at  the  will  of  the  operator, 
and  its  ability  to  yield,  in  setting  up,  a  monolithic  mass.  The 
strength  of  any  concrete  is  necessarily  dependent  upon  its  constituent 
materials — rock,  sand  and  cement.  The  mortar  must,  in  a  plastic 
state,  be  sufficient  to  not  only  fill  the  voids  in  the  rock,  but  to  also 
coat  each  surface.  The  rock  must  be  possessed  of  sufficient  strength 
in  itself,  and  the  mortar  must  be  of  such  strength  as  to  thoroughly 
cement  the  rock  together.  It  is  evident,  therefore,  that  the  mortar 
is  the  vital  constituent  of  a  concrete.  The  proper  proportioning  of 
the  mortar,  and  its  mixing  with  the  rock,  constitute  the  "Knowing 
how"  of  concrete.  The  rock  and  sand  constitute  the  chemically  inert 
portion  of  a  concrete  and  are  termed  the  aggregate. 

Difference  between  "Rock"  and  "Sand."     Any  mineral  detritus  Difference 
finer  than   %"  is  called  sand,  and  that  portion  coarser  than  %"  between 
is  called  rock  (or  gravel).  rock  and  sand 


18 GOOD  CONCRETE 

ROCK. 

Kinds        Under  the  head  of  rock  will  be  considered  all  of  the  aggregate, 
of  rock  be  it  artificially  crushed  or  natural,  which  is  coarser  than  %". 

The  "Rocks"  most  usually  crushed  for  concrete  aggregates  are: 
Trap,  limestone,  granite,  sandstone,  basalt  and  conglomerate.  Slates 
and  shales  are  not  adapted  to  the  purpose  on  account  of  their  lack 
of  strength. 

Trap  and  Limestone  of  dense  textures  are  considered  the  best 
materials  for  the  purpose,  as  they  are  strong  and  crush  to  more  or 
less  cubical  fragments. 

Granite  and  basalt  are  not  so  well  suited  for  aggregate  as  they 
are  likely  to  break  into  spawls  or  flat  pieces,  which  become  trouble- 
some in  tamping  the  concrete  due  to  their  tendencey  to  "arch"  and 
produce  pockets. 

Sandstone  is  rather  too  porous  to  be  classed  as  a  first  class  aggre- 
gate. Conglomerate,  if  possessed  of  a  cubical  cleavage,  makes  a 
good  aggregate. 

Cinders  and  old  brick  are  in  some  cases  used  as  aggregate.  The 
cinder  must  be  free  from  unburnt  or  partially  burned  coal  and  reason- 
ably free  from  sulphur. 

Old  brick,  if  thoroughly  wet  before  using  with  the  sand  and 
cement,  can  be  used  to  good  advantage  where  no  great  loads  are 
to  be  carried. 

Both  cinder  and  old  brick  are  considerably  lighter  in  weight  than 
rock  and  are  well  adapted  to  use  when  lightness  with  reasonable 
strength  is  required. 

The  selection  of  a  rock  for  the  aggregate  will,  of  course,  be  gov- 
erned by  local  conditions,  by  what  the  locality  offers,  and  the  im- 
portance of  the  work.  In  the  majority  of  Southern  California  locali- 
ties stream  gravel  is  available  in  almost  unlimited  quantities.  // 
proper/];  screened,  this  material  makes  an  excellent  coarse  aggregate. 


GOOD  CONCRETE 19 

The  practice  of  using  the  natural  gravel  and  sand  just  as  it  comes  Danger  of 
from  the  stream  is  an  exceedingly  poor  one.     Whereas  the  gravel  "' 
and  sand  may  be  in  themselves  of  excellent  quality,  they  are  seldom,  "' 
if  ever,  found  in  exactly  the  proper  proportions.     Furthermore,  the 
proportion  of  sand  and  gravel  are  different  for  nearly  every  foot  of 
depth,  so  that  it  is  nearly  impossible  to  get  two  successive  wagon- 
loads  that  are  the  same. 


SIZES  OF  ROCK. 

The  largest  size  of  rock  allowable  in  concrete  will  depend  en-  Cyclopean 
tirely  upon  the  nature  of  the  work.      For  massive  work,   such  as  concrete 
foundations,   dams,   etc.,   3J/i"   for  the  concrete  proper,  and  it  is 
customary  and  good  practice  to  imbed  in  the  concrete  stone  up  to 
1  cu.  ft.  in  size  as  "displacers."     This  is  termed  "Cyclopean  Con- 
crete."    In  some  very  large  dams  "displacers"  of  one  ton  weight 
have  been  successfully  used. 

For  reinforced  concrete   1"  is  the  largest  size  allowable. 


EFFECT  OF  SIZE  OF  ROCK  UPON  THE  STRENGTH  OF 
CONCRETE. 

From  a  purely  theoretic  standpoint  it  would  seem  that  the  larger  Effect  of 
the  rock  in  a  concrete  the  greater  the  strength,  as  there  is  less  sur-  size  of  rock 
face  to  cover  while  the  percentage  of  voids  remains  practically  the  uP°n  strength 
same.      But  practical  considerations  of  placing  and  compacting  the 
concrete  considerably  modify  this  view.     If  the  stone  is  too  large 
trouble  is  experienced  in  properly  tamping.     General  Gillmore  at  the 
Watertown  Arsenal  made  a  series  of  tests  to  demonstrate  this  point. 


20 


GOOD  CONCRETE 


TESTS  OF  1:1:3  CONCRETE  MADE  OF  DIFFERENT  SIZES  OF 
ROCK. 


Size  of  Rock 

Age,  Days 

Weight 
per  cu.  ft. 

Compressive  Strength 
Ibs.  per  sq.  in. 

W  Trap 

32 

146.4 

2800 

%"  Trap 

32 

148.3 

3200 

1     "Trap 

34 

160.9 

4917 

1M"Trap 

41 

161.2 

4562 

2K"  Trap 

32 

161.4 

4140 

#"  Gravel 

34 

147.0 

2992 

IK"  Gravel 

29 

151.5 

3817 

3    "Gravel 

41 

153.6 

4200 

CRUSHED  ROCK  vs.  GRAVEL. 

Crushed        Much  has  been  said  and  written  about  the  relative  merits  of  these 

rock  or   two  materials  as  coarse  aggregates  for  concrete.      Some   engineers 

gravel    contend  that  crushed  rock  made  of  hard,  unweathered  and  durable 

stone  is  far  superior  to  gravel,  basing  their  contention  on  the  fact  that 

crushed  rock  has  a  rough  crystalline  surface,  which  greatly  increases 

the  adhesion  of  the  mortar  to  the  rock  particles,  while  gravel  presents 

a  round  and  smooth  surface. 

Aside  from  any  preconceived  preferences,  the  choice  of  the  two 
materials  can  safely  be  left  to  their  cost.  There  have  been  as  many 
notable  concrete  structures  built  of  crushed  rock  as  there  have  been 
of  gravel.^  Gravel  by  the  nature  of  its  occurrence  is  the  "Survival  of 
the  fittest";  it  represents  the  most  refractory  portions  of  the  rock 
from  which  it  has  been  derived. 

On  close  examination  of  any  of  the  Pacific  Coast  gravels  it  will 
be  seen  that  the  surface  is  covered  with  minute  "pit  marks,"  which 
can  safely  be  relied  upon  to  give  all  the  necessary  adhesion  between 
it  and  the  mortar. 


GOOD  CONCRETE 21 

Either  material  must  be  free  from  surface  coatings  of  foreign 
substances. 

SAND. 

Sand  is  an  unconsolidated  debris  resulting  from  the  weathering 
and  decomposition  of  rock.  It  is  composed  of  grains  of  varying  size 
and  shape. 

It  can  be  derived  from  any  rock  and  will  therefore  possess  charac-   ,/Vo  two 
teristics  as  widely  different  as  those  of  the  rocks  from  which  it  origi-   sands 
natcd.  are  alike 

All  sands  therefore  will  not  be  of  equal  value  as  aggregate.  Sands 
which  to  the  eye  may  seem  identical  can  be  found  upon  testing  to 
be  greatly  dissimilar  in  their  value  as  ingredients  of  mortar  or  con- 
crete. In  fact,  sands  from  the  same  pit  show  enormous  variations 
in  sizing  of  grains. 

Sands  are  distributed  in  nature  by  rivers  and  streams. 

The  size  of  grains  that  can  be  transported  by  flowing  water  is  a    /^j'ver 
function  of  its  velocity.     A  torrent  will  carry  coarse  sand  and  gravel    ana 
until  its  velocity  is  suddenly  checked,  as  by  an  abrupt  bend  in  the    Creek 
channel,  at  which  point  it  deposits  the  coarser  particles  while  the  finer    sands 
ones  stay  in  suspension.     As  the  velocity  of  the  moving  water  grows 
less,  finer  material  is  deposited  until  in  slowly  moving  streams  only 
silt   is  dropped.      It  is  in  the  bends  of  old   stream  channels  that 
"Gravel  Pits"  are  found. 

Bank   sands   are   deposited  at  periods   of   high   water   along   the    Bank 
banks  and  stream  terraces.     Such  sands  are  usually  quite  uniform  in    sands 
their  sizing,  but  under  some  circumstances  carry  a  large  percentage 
of  foreign  matter. 

On  the  other  hand,  sands  taken  from  the  beds  of  streams  in  the    All  sands 
dry  season  show  great  variations  in  the  sizing  of  their  grains.      In    van;  in 
localities  where  stream  beds  furnish  the  supply  of  sand  and  gravel    composition 
many  of  the  failures  of  concrete  work  are  attributed  to  the  cement 
used,  when  in  reality  the  sand  is  responsible. 


22  GOOD  CONCRETE 

It  is  evident  that  a  stream  that  goes  dry  at  some  season  must  at 
others  carry  a  great  volume  of  water  with  varying  velocities  which 
will  deposit  layers  of  very  dissimilar  sized  sand.      It  is  the  indis- 
criminate use  of  these  different  sized  sands  that  is  responsible  for  a 
great  deal  of  the  wretched  work  done  in  our  small  towns. 
Sands      Sand  cannot  be  properly  judged  by  simply  looking  at  it.     It  must 
must  be  be  examined  by  the  proper  method  to  establish  its  value  for  the  in- 

tested  tended  purpose. 

Hol»  to      To  establish  the  characteristics  of  any  sand,  it  is  examined  for: 
test  sands  (1)      Strength  of  grains 

(2)  Cleanness  or  freedom  from  clay,  loam,  dirt 

and  organic  matter. 

(3)  Sizing  of  particles  or  Mechanical  Analysis 

(4)  Weight  per  cubic  foot 

(5)  Per  cent  of  voids. 

Grain       (1)      A  mortar  cannot  be  any  stronger  than  its  weakest  cora- 
strength  ponent.     It  is  necessary,  therefore,  to  select  a  sand  whose  grains 
are  of  sufficient  strength. 

Sands  whose  grains  can  be  easily  crushed  by  rubbing  between 
the  palms  of  the  hands  or  by  slight  pressure  are  not  fit  for  use. 

Sands  that  soften  when  placed  in  water  or  impart  to  it  a  perma- 
nent turbidity  are  to  be  avoided.  To  this  class  belong  those  sands 
derived  from  chalks  and  shales. 

Quartz  sands  as  a  general  rule  are  preferable  to  all  others.  They 
contain  less  decomposed  mineral  matter  and  have  great  grain  strength. 

Sands  derived  from  dense  crystalline  limestones  are  also  considered 
excellent  material.  Artificial  sand  or  screenings  made  in  crushing  a 
durable  crystalline  limestone  are  by  some  authorities  considered  su- 
perior to  all  other  sands  if  they  do  not  contain  too  much  fine  dust. 

Dirty       (2)      Sands  containing  clay,  loam,  dirt  and  other  organic  matter 
sands  should  be  avoided.     Such  sands  might  be  improved  by  washing,  but 

this  procedure   may  be  more  expensive  than  getting  a  clean   sand 

from  some  ether  locality. 


GOOD  CONCRETE 23 

In  working  up  a  mortar  made  from  a  dirty  sand,  the  clay  and  Dirty 
loam  "slimes"  and  envelops  the  sand  grains,  thus  preventing  a  bond  sands  are 
between  the  grains  and  the  cement  grout.  dangerous 

These  foreign  substances  also  exert  a  marked  influence  upon  the  Dirty  sands 
setting  of  the  mortar.     They  greatly  retard  the  hardening,  and  can,   affect  the 
in  fact,  under  some  circumstances  entirely  prevent  it.  hardening 

The  following  simple  methods  are  very  effective  in  determining 
the  cleanness  of  a  sand: 

Rub  some  of  the  sand  between  the  palms  of  the  hands.     If  they  Hov>  to 
are  badly  discolored  the  sand  is  "dirty."  tell  a 

Into  a  pail  full  of  clear  water  drop  a  handful  of  the  sand.     If  dlrt^  sand 
the  bottom  of  the  pail  is  visible  at  the  end  of  two  minutes  the  sand  is 
considered  clean. 

Take  a  quart  fruit  jar,  fill  it  one-quarter  full  of  sand,  then  pour 
in  water  until  three-quarters  full,  screw  on  the  top  and  shake  vigor- 
ously for  a  minute  and  allow  to  settle.  If  a  layer  of  mud  settles 
over  the  sand,  it  is  "dirty"  and  should  not  be  used  without  being 
washed. 

The  presence  of  organic  matter  is  usually  in  the  form  of  soil  humus,   Soil 
decayed  vegetable  matter  and  mould.     These  substances  form  a  soap-  humus 
like  compound  with  the  lime  in  a  cement  and  produce  disintegration,    in  sands 

(3)      Sizing  of  Particles: — Of  decided  influence  upon  the  strength  Sands 
of  a  mortar  is  the  sizing  of  the  sand  grains.     It  is  a  well-known  fact  must 
that  coarse  sands  give  stronger  mortars  than  fine  ones.     The  reason   have 
for  this  will  be  apparent  if  we  consider  the  following:     If  we  assume,   proper 
for  the  sake  of  calculation,  that  each  sand  grain  is  a  sphere,  then  sizing 
each  sphere  of  the  same  diameter  will  have  a  definite  surface  area.    °f 
To  separate  a  sand  into  various  sizes,  all  that  is  necessary  is  to  pass 
it  through  a  given  sieve.     For  instance,  if  we  pass  a  material  through 
the  sieve  having  200  holes  per  linear  inch  (40,000  per  sq.  in.),  the 
average  diameter  will  be  0.0027".     Now  to  count  the  number  of 
sand  grains  in  a  cubic  yard  of  200  mesh  material  we  simply  divide 


GOOD  CONCRETE 


36"  by  .0027  and  cube  the  quotient.  Then  by  applying  the  factor 
of  surface  area  we  have  the  total  surface  of  grains  in  a  cubic  yard. 
Carrying  out  the  computation  for  the  No.  200,  No.  1 00,  No.  50, 
No.  20,  No.  1 0  and  No.  4  sieves,  we  get  the  relative  surface  area 
in  a  cubic  yard  of  each  of  these  sizes.  The  results  thus  obtained 
are  rather  surprising. 

TABLE  I. 

SHOWING  RELATION  BETWEEN  DIAMETERS  AND  TOTAL 
SURFACE  AREAS  IN  ONE  CUBIC  YARD  OF  MATERIAL: 


Diameter  of  Grain 

Sieve  Number 

Surface  to  covet 
in  1  cu.  yd. 

.0027 

200 

41,500sq.yds. 

.0045 

100 

25,1  30  sq.  yds. 

.011 

50 

1  0,500  sq.  yds. 

.034 

20 

3,325  sq.  yds. 

.073 

10 

l,620sq.  yds. 

.22 

4 

5  18  sq.  yds. 

Why  a  fine       From  the  above  table  it  is  very  evident  why  a  fine  sand  cannot  be 
sand  is  as  stronS  m  a  mortar  mixture  as  a  coarse  one,  when  mixed  with  the 
not  good  same  percentage  of  cement. 

Consider  a  1  :3  mortar  made  of  \'\"  grains.  Such  a  mortar  has 
518  sq.  yds.  of  surface  per  cu.  yd.,  while  one  made  of  sand  of  the 
No.  1 0  size  has  1 620  sq.  yds.  of  surface  to  cover  with  cement  grout 
in  a  cubic  yard.  In  other  words,  the  No.  1 0  sand  will,  according 
to  our  calculations,  take  nearly  three  times  as  much  cement  to  produce 
a  mortar  of  the  same  strength  as  the  1  :3  No.  4  mortar. 

In  practice,  however,  we  cannot  figure  as  close  as  this,  as  no  sands 
are  composed  of  one  size,  but  of  a  great  many  different  ones.  There 
is,  however,  a  very  close  connection  between  the  figures  produced  and 
the  results  obtained  in  practice. 


GOOD  CONCRETE 


25 


TABLE  II. 

TESTS  SHOWING  EFFECT  OF  SIZE  OF  GRAIN  ON  STRENGTH  OF 
MORTAR. 

Mechanical  Analyses: 


Per  Cent  Passing  Given  Sieve 

Compressive  Strength 
Lb*.  PerSq.  In.of  1:3 
Mortar  at  2  Mot. 

No. 

4 
100 

10 

20 
46 

30 
33.5 

50 
21.0 

60 

100 

200 

1 

79 

1.7 

0.8 

.0 

3627 

2 

100 

99.5 

98.5 

96.7 

82 

75.5 

30.0 

3.1 

844 

Sand  No.    1    is  a  bank  sand  from  near  Yuma,  Arizona,  used 
on  the  Laguna  Dam. 

Sand  No.   2  is  from  the  Colorado  River  near  Laguna,  Arizona. 

Mechanical  Analysis: — The  separating  of   a  sand   into  various 
sizes  by  means  of  different  sieves  is  called  "Mechanical  Analysis." 


TABLE  III. 


TABLE  OF  SIEVES  AND  THEIR  MESHES:                    How  the 

Sieve  No. 

4 

16 

0.22 

10 

20 

30 

40 

50 

100 

200      the  grains 

Opening,  per 
tq.  m. 

Size  of  opening 

100 
0.073 

400 
0.034 

900 
0.024 

1600 
0.017 

2500 
0.014 

10000 
0.0055 

40000     IS  ^e'erm'ne^ 
0.0027 

For  this  test  a  set  of  sieves,  Nos.  4,  1 0,  20,  30,  40,  50,  1 00  and 
200,  is  necessary.  The  sieve  numbers  give  the  number  of  holes  per 
linear  inch.  The  sieve  should  be  about  8"  in  diameter.  They  can 
be  had  from  any  "Assayer  Supply"  house. 

To  make  test:  Weigh  out  any  even  number  of  Ibs.  of  sand  (sand 
must  be  dry).  Place  on  No.  4  sieve,  shake  until  no  more  passes, 
weigh  what  has  passed  and  record  weight  in  ounces.  Take  this 
portion  that  has  passed  the  No.  4  and  sieve  it  through  a  No.  1 0. 


26 GOOD  CONCRETE 

Weigh  passed  portion  and  record  in  ounces.  Repeat  this  for  each 
sieve,  taking  the  portion  that  passed  the  previous  sieve. 

Wt.  passing  that  sieve  (in  ozs.) 

Then  %  passing  any  No.  sieve  -  -  — X 1 00 

Wt.  taken  for  test  (in  ozs.) 

If  the  metric  system  of  weights  is  used  the  computations  will  be 
eliminated;  the  weighing  will  give  the  per  cent  direct  if  1000  grms. 
of  the  sample  are  used  for  the  test. 

The  strength       In  order  to  compare  different  mechanical  analyses  it  is  a  great 
of  a  convenience  to  plot  the  results  in  a  curve  or  diagram.    Squared  paper 
concrete  is  used,  laying  off  on  the  horizontal  lines  the  diameter  corresponding  to 
is  controlled  sieve  openings,  and  on  the  vertical  lines  the  %  of  the  material  passing 
by  the  any  given  sieve.     The  points  thus  established  are  joined  by  straight 
sizing  of  lines,  and  the  figure  thus  produced  is  called  the  "Mechanical  Analysis 
grains  Curve,"  or  M.  A.  Curve.     These  curves  are  very  useful  in  the  appli- 
cation of  the  "Concrete  Lav>."     The  form  of  the  M.  A.  Curve  is 
an  index  to  what  may  be  expected  from  a  given  sand  as  to  compres- 
sive  strength. 


GOOD  CONCRETE 


27 


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28 


GOOD  CONCRETE 


Plate  I 


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Medanical  Analyses  of  /^/w«cs  Jw^  5ho*>iny  Relation 

of  M.A-  Curves  <5-  Compress  ive  Strength  of  /.-3  Morters 


GOOD  CONCRETE 


29 


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Mechanical  Analyses  of  Various    Rock  Screenings 
Showing  Relation  of  M.A.Curves  to  Compress!  ve  Strength  oj  /--3  Mortars 

30  GOOD  CONCRETE 

The  data  in  Table  IV.  is  arranged  from  an  elaborate  series  of 
test  on  sands  and  screenings  by  the  U.  S.  Geological  Survey  (Bui. 
331). 

The  mechanical  analyses  are  plotted  in  Plates  I  and  II  by  the 
method  explained  above.  These  M.  A.  curves,  or  diagrams,  are 
worthy  of  close  study.  Starting  with  the  M.  A.  Curve  of  sands  1 
and  2  and  going  to  sand  No.  8,  there  are  represented  eight  types 
of  sizing. 

Fine  sands  have  a  characteristically  sharp  curve  like  Nos.  1  and  2, 
and  as  the  coarseness  of  grain  increases  the  curve  becomes  flatter. 
Thus  sands  3  and  4  have  flatter  curves  than  sands  1  and  2 ;  Nos.  5 
and  6  are  flatter  than  3  and  4,  and  7  and  8  are  flatter  than  5  and  6. 
The  compressive  strength  of  1  :3  mortar  from  each  of  these  sands  at 
three  months  is  shown  en  each  diagram. 

Screenings       It  will  be  noticed  that  the  compressive  strength  increases  as  the 

follow  a  curves  flatten  out.     It  will  also  be  noticed  on  inspection  of  the  50- 

different  mesh  column  of  Table  IV  that  generally  the  less  the  percent  of  grains 

rule  of  passing  the  No.  50  sieve  the  greater  the  compressive  strength.     This 

sizing  fact  holds  only  for  sands,  and  not  generally  for  screenings. 

It  must  be  borne  in  mind  that  sands  usually  have  round  grains, 
and  screenings  more  angular  ones. 

The  M.  A.  Curve  is  a  diagram  showing  the  size  of  grains  and  the 
percent  of  these  sizes ;  and  each  material  will  have  a  typical  M.  A. 
curve.  In  fact,  these  principles  have  been  worked  out  so  generally 
that  from  them  is  derived  the  "Concrete  Law,"  which  will  be  con- 
sidered at  another  place. 

Screenings       Sand  vs.  Rock  Screenings: — Screenings  from  crushed  rock  are  an 
make  good  artificial  sand.     The  use  of  this  material  in  place  of  sand  is  universal 
fine  aggregate  in  some  portions  of  the  U.  S.  and  quite  general  in  Europe. 

There  are  quite  a  number  of  factors  that  make  screenings  superior 
to  sand.  Principally  the  sizing  of  the  grains,  and  their  angularity 
make  it  possible  to  obtain  a  greater  density  of  mortar,  although  as  a 


GOOD  CONCRETE 31 

general  rule  screenings  contain  more  voids  than  sand.  Limestone 
and  trap  rock  screenings  are  far  superior  to  screenings  from  any  other 
rocks.  The  grains  of  these  materials  are  more  nearly  cubical.  Other 
rocks  are  likely  to  give  flat  grains  that  will  not  compact  well. 

The  prejudice  against  rock  screenings  by  some  constructors  and 
engineers  is  based  on  sound  reasons,  namely  that  the  screenings  con- 
tain all  the  quarry  "dirt"  that  occurs  in  the  seams  of  the  rock  in  place 
and  also  a  great  deal  of  the  "muck"  that  is  shoveled  up  with  the  rock 
in  the  quarry  and  passes  through  the  crusher  and  the  screens. 

Aside  from  these  objections  it  can  safely  be  said  that  clean  screen- 
ings are  a  worthy  competitor  of  sand. 

In  screenings  there  is  usually  a  higher  percent  of  "fines"  (material  "Fines"  in 
finer  than  50  mesh)  than  is  found  in  good  sands.    Applying  the  gen-  screenings 
eral  rule  for  sand,  that  fine  material  is  objectionable,  screenings  would 
be  discredited. 

Experience  and  elaborate  tests  have  shown  that  this  is  not  the 
case.  The  reason  that  the  "fines"  in  the  screenings  are  not  detri- 
mental is  probably  a  chemical  one.  It  is  a  well-known  fact  that 
limestone  and  trap  rock  dust  will  bind  together  macadam,  acting  as 
a  cement,  and  it  is  probable  that  in  a  mortar  made  of  screenings  we 
have  the  strength  of  the  cement  plus  the  strength  of  the  binding  action 
of  the  screenings. 

Plate  II  shows  the  M.  A.  curves  of  seven  types  of  screenings. 
These  results  are  contained  in  Table  IV  and  are  from  the  same  series 
of  tests  by  the  U.  S.  Geological  Survey  as  those  mentioned  above. 

The  U.  S.  Reclamation  Service  has  used  rock  screenings  on  a 
number  of  their  projects  with  excellent  results. 

To  Determine  the  %  of  Voids: — The  voids  in  a  sand  or  rock  Voids 
may  be  defined  as  the  amount  of  space  between  the  grains.     A  short,  and 
but  not  very  accurate,  method  to  determine  this  is  to  see  what  amount  hon>  to 
of  water  the  sand  will  absorb.      The  chief  objection  to  this  method  determine 
is  that  water  will  shove  the  sand  grains  apart,  and  thus  give  too  high  them 
a  percent  of  voids. 


GOOD  CONCRETE 


Solid        The  most  accurate  method  is  to  find  the  difference  in  weight  be- 
rock   tween  a  cubic  foot  of  solid  rock  of  the  same  specific  gravity  as  the 
sand  or  rock  and  its  weight  per  cubic  foot  in  the  loose  state. 

Since  the  specific  gravity  of  a  substance  is  its  weight  compared 
ta  the  weight  of  an  equal  volume  of  water,  then  the  weight  of,  say, 
a  cubic  foot  of  rock  solid,  will  be  the  weight  of  a  cubic  foot  of  water 
(62.3  Ibs.)  multiplied  by  the  specific  gravity  of  the  rock. 

The  average  specific  gravity  of  sand  is  2.65.     Now  to  compute 
the  voids  in  a  cubic  foot  of  sand  proceed  as  follows: 
Make  a  box  12"x12"x12"  and  weigh  it. 
Fill  it  with  sand  and  weigh  it. 
From  this  weight  subtract  the  weight  of  the  box  and 

call  it  the  net  weight  of  the  sand. 
Then  62.3  X2.65=165=wt.  of  cu.  ft.  of  solid  rock, 
(wt.  of  cu.  ft.  of  the  sand) 


Then      1- 


165 


X  1 00    %  of  voids. 


TABLE  V. 

TABLE  OF  SPECIFIC  GRAVITIES  AND  WEIGHT  OF  1  Cu.  FT. 
SOLID. 


Sand 

Gravel 

Limestone 

Trap 

Granite 

Spec.  Gr. 

2.65 

2.66 

2.60 

2.90 

2.70 

Wt.  per  cu. 

ft.  solid 

165  Ibs. 

165  Ibs. 

162  Ibs. 

180  Ibs. 

168  Ibs. 

Table  V  will  be  found  convenient  in  computing  the  %  of  voids  of 
sands,  gravel,  crushed  rock  and  crushed  rock  screenings. 


GOOD  CONCRETE 


33 


TABLE  VI. 
VOIDS  FOR  DIFFERENT  WEIGHTS  PER  Cu.  FT. 


Per  Cent  of  Voids 


Wt.  per  cu.  tt, 
loose  (1) 

Sand 

Grave! 

Limestone 

Trap 

Granite 

(2) 

(3) 

(4) 

(5) 

(6) 

75  Ibs. 

55 

55 

54 

59 

55 

801bs. 

52 

52 

51 

56 

52 

85  Ibs. 

49 

49 

48 

53 

50 

90  Ibs. 

46 

46 

46 

50 

47 

95  Ibs. 

42 

42 

41 

47 

44 

100  Ibs. 

39 

39 

38 

45 

41 

105  Ibs. 

36 

36 

35 

42 

38 

110  Ibs. 

33 

33 

32 

39 

35 

115  Ibs. 

30 

30 

29 

36 

32 

120  Ibs. 

27 

27 

26 

31 

29 

125  Ibs. 

24 

24 

23 

28 

26 

130  Ibs. 

21 

21 

20 

25 

23 

135  Ibs. 

18 

18 

17 

23 

20 

Table  VI  gives  the  voids  corresponding  to  the  weight  per  cu.  ft. 
of  sands,  gravels,  crushed  limestone,  trap,  granite  and  their  screen- 
ings. These  figures  are  based  on  dry  material;  they  do  not  hold 
for  damp  or  wet  conditions.  If  the  material  is  damp  and  wet  it 
should  be  spread  out  in  the  sun  to  air  dry  before  taking  the  weight 
per  cu.  ft. 

Example: — In  the  first  column  are  given  the  weights  per  cu.  ft. 
Suppose  a  sand  was  found  to  weigh  95  Ibs.  cu.  ft.  In  Col.  1  find 
95,  and  opposite  it,  under  column  headed  "Sand,"  will  be  found 
the  %  voids,  which  for  this  particular  case  will  be  42%.  The 
same  procedure  is  followed  for  crushed  rock  and  screenings. 


GOOD  CONCRETE 


Density  Density  of  a  Mortar: — By  this  term  is  meant  the  degree  to  which 
the  voids  in  a  sand  are  filled  with  cement  paste.  If,  for  example,  a 
cubic  foot  of  sand  was  found  to  weigh  1 1 5  IBs.,  then  from  Table  VI 
we  know  that  it  contains  30%  voids,  or  0.3  of  a  cu.  ft.  of  spaces 
that  are  to  be  filled  with  cement  paste,  to  make  it  as  dense  as  possi- 
ble. If  a  mortar  has  all  of  the  voids  filled  it  is  said  to  have  a  density 
equal  to  1 .0.  If  all  the  voids  are  not  filled,  then  the  density  will  be 
less  than  I.  If  the  voids  are  more  than  filled  the  density  will  be 
greater  than  1. 

Cement       Cement  Paste: — Dry  neat  cement  has  no  binding  pou>er....  It  must 

paste  first  be  converted  into  a  paste  before  it  becomes  capable  of  cementing 

and  sand  grains  together.     Now  in  converting  a  cu.   ft.  or  one  sack  of 

r»ater-tighlness  cement  into  a  paste  by  the  addition  of  the  proper  amount  of  water 

and  thoroughly  mixing,  it  will  be  found  that  a  shrinkage  of  about 

15%  takes  place.     A  cubic  foot  (1  sack)  will  therefore  yield  about 

.85  of  a  cubic  foot  of  paste,  and  in  the  proportioning  of  mortar  it  is 

the  amount  of  cement  paste  and  not  of  dry  cement  that  should  be 

used  to  determine  the  densest  mixture.     This  fact  is  of  the  utmost 

importance  in  making  watertight  or  impermeable  mortar. 

Consider,  again,  a  sand  weighing  1  1 5  Ibs.  per  cu.  ft.  with  voids 
equal  to  30%.  Then  1  cu.  ft  of  the  sand  contains  0.3  cu.  ft.  of 
voids.  Now  to  make  the  densest  mortar  we  will  not  need  0.3 
cu.  ft.  of  dry  cement,  but  will  need  15%  more  cement.  That  is, 
instead  of  0.3  cu.  ft, 

(0.3  0.3     x     0.15)     =     0.345  cu.  ft 

of  dry  cement  will  be  needed. 

How       Yield  of  Mortar: — The  cement  user  is  of  course  interested  in 
much  knowing  how  much  mortar  a  given  quantity  of  sand  and  cement 
mortar  will  make. 

One  cubic  foot  of  cement  and  two  cubic  feet  of  sand  will  not 
give  1+2=3  cu.  ft.  of  mortar,  but  considerably  less. 

Under  "Density  of  Mortar"  it  has  been  explained  what  relation 
the  voids  have  to  a  mortar. 

The  following  table  is  computed  on  the  basis  that  1  sack  of  cement 
gives  .85  cu.  ft.  of  cement  paste: 


GOOD  CONCRETE 


35 


TABLE  VII. 
AMOUNT  OF  PLASTIC  MORTAR  FROM  1  SACK  OF  CEMENT. 


Proportion 

Voids  in  Sand 

Cement 
Sacks 

Sand 

Cu.  Ft. 

25% 

30%  |  35% 

40% 

45% 

50% 

Cubic  Feet 

1 

1.60 

1.55 

1.50 

1.45 

1.40 

1.35 

IH 

1.97 

1.90 

1.83 

1.76 

1.69 

1.62 

2 

2.35 

2.25 

2.15 

2.05 

1.95 

1.85 

2H 

2.72 

2.60 

2.48 

2.36 

2.24 

2.12 

3 

3,10 

2.95 

280 

2.65 

2.50 

2.35 

31A 

3.47 

3.40 

3.12 

2.90 

2.77 

2.55 

36 


GOOD  CONCRETE 


Plate  ILL 
Illustrating  the  Grading 
of  Jf'zes  in  a  Concrete 


a  =  Very  poor -5izinq 
*•-  Ufter  „  * 
C  =  exce//e/rf 


CHAPTER  III. 


PROPORTIONING  CONCRETE. 

Concrete  has  already  been  defined.  The  methods  of  proportion- 
ing will  now  be  considered. 

The  proportions  are  usually  stated  as  so  many  parts  cement  to  How  is 

so  many  parts  sand  to  so  many  parts  rock  or  gravel.     Thus  a  1-2-4  concrete 

mixture  means   1   part  cement  to  2  parts  sand  and  4  parts  rock  or  proportioned 
gravel. 

To  arbitrarily  specify  the  proportions,  as  1-2-4,  1-3-6,  etc,  for 
any  particular  work  without  regard  to  the  voids  in  the  sand  and  rock 
and  gravel  and  to  the  grading  of  their  sizes,  is.  to  say  the  least,  a 
very  primitive  method. 

Crushed  rock  and  sand  vary  widely  in  their  percent  of  voids  and 
the  grading  of  the  sizes  of  their  particles. 

In  order  to  properly  balance  the  cement,  sand  and  rock,  the  factor 
of  voids  and  sizes  must  be  considered. 

Three  methods  of  proportioning  are  now  used: — 

( 1 )  Proportioning  by  taking  into  consideration  the 

voids  in  the  sand  and  rock. 

(2)  Proportioning  by  trial,  varying  the  parts  of 

sand  and  gravel,  until  the  densest  mortar  is 
obtained. 

(3)  By  the  "Concrete  Law"  which  takes  into  con- 

sideration the  grading  of  sizes. 


38  GOOD  CONCRETE 

(0 

Proportioning  by  Voids: — The  voids  in  the  rock  are  determined 
either  by  observing  the  amount  of  measured  water  that  a  given  vol- 
ume will  absorb,  or  by  taking  the  weight  per  cubic  foot  and  using 
Table  VI  to  find  the  voids.  The  voids  thus  determined  plus  10% 
will  be  the  volume  of  mortar  necessary  to  fill  all  the  voids  in  the 
rock  and  produce  a  dense  concrete. 

The  voids      The  amount  of  cement  necessary  for  the  mortar  will  of  course 
must  be  depend  upon  the  voids  in  the  sand,  and  the  purpose  for  which  the 
fitted  concrete  is  to  be  used. 

The  proportion  of  cement  should  never  be  less  than  the  voids  in 
the  sand. 

Other  things  being  equal,  the  strength  of  a  mortar  will  vary  directly 
as  the  percent  of  cement  in  it  For  work  requiring  great  strength 
it  is  customary  to  use  mixture  of  1  cement  to  1  sand.  This  is  par- 
ticularly the  case  in  reinforced  concrete  columns.  It  must  be  borne 
in  mind  that  the  strength  of  the  mortar  is  the  factor  that  determines 
the  strength  of  the  concrete. 

Rule  for      Where  no  great  accuracy  is  required  a  convenient  rule  for  pro- 
finding  portioning  is  as  follows: 

best       (a)      Take  a  clean  bucket  and  determine  its  volume  by  pouring 
mix  in  a  measured  amount  of  water. 

(b)  Fill  the  bucket  up  level  with  rock;  pour  in  a  measured 
amount  of  water  until  the  water  comes  to  the  surface. 

(c)  The  measured  amount  of  water  plus    10%    will   be  the 
amount  of  sand  necessary. 

(d)  Take  one  bucket  of  rock  and  mix  with  it  the  amount  of  sand 
determined  in  (c)  ;  place  back  into  the  bucket  this  mixture. 

(e)  Pour  in  a  measured  amount  of  water  on  the  mixture  until 
the  water  comes  to  the  surface. 

The  amount  of  water  taken  will  be  the  volume  of  voids  left  in  the 
mixture,  and  this  volume  plus  15%  will  be  the  amount  of  cement  to 
use. 


GOOD  CONCRETE  39 

The  proportion  determined  by  this  rule  will  be  found  to  give  an 
excellent  concrete,  providing  the  sand  and  rock  conform  with  the 
requirements  of  good  materials  as  set  forth  under  "sand  and  rock." 

(2) 

Proportioning  by  Trial: — This  method  has  for  its  object  the  de- 
termination of  the  best  mixture  that  can  be  made  from  a  fixed  pro- 
portion of  cement  to  aggregate. 

For  example,  let  a  specified  proportion  of  1  cement  to  6  aggregate 
be  considered;  that  is,  1  :6. 

The  proportion  of  1 :6  can  mean  a  number  of  different  proportions  Hoiv 
of  sand  to  rock.  much  sand 

Thus  it  can  mean      :l:5 

:  1/2:41/2 
:2:4 

:2'/2:3'/2 
or  :3:3 

The  sum  of  the  sand  and  rock  adding  up  to  6  in  each  instance. 
Which  one  of  these  mixtures,  then,  will  give  the  best  concrete? 

It  has  been  well  established  by  many  tests  on  large  construction 
projects  that: 

For  any  fixed  proportion  of  cement  to  aggregate  that  combina-  Best  mix 
tions  of  sand  and  rock,  which,  with  the  fixed  amount  of  cement,  give  for  a  given 
the  smallest  volume  of  plastic  concrete,  will  give  the  densest  mixture,  proportion 
and  incidentally  the  strongest,  easiest  compacting  and  quickest  hard- 
ening. 

Take  a  piece  of  steel  casing  6"  in  diameter  and  1 0"  long,  plugged 
at  one  end. 

Lay  off  on  a  stick  the  clear  inside  depth.  Divide  this  length  into 
as  many  equal  parts  as  there  are  units  in  the  sum  of  cement  and  ag- 
gregate. Thus  if  the  specified  proportion  is  1  :6,  lay  off  (1+6)  =7 
equal  divisions  on  the  length. 


GOOD  CONCRETE 


Then  make  up  a  trial  unit,  say,  of 

1  cem.  1J/2  sand,  4]/z  rock,  by  measuring  out  the  quantities  in 
the  cylinder,  by  means  of  the  divided  stick. 

Convert  this  mixture  into  a  concrete  by  first  thoroughly  mixing  dry 
and  then  adding  enough  water  to  give  a  consistency  of  soft  "puf/p." 
Tamp  this  concrete  into  the  cylinder  and  measure  its  volume  by 
means  of  the  stick.  Note  this  volume. 

Then  make  up  another  mix,  say,  of  1  :2:4,  and  so  on,  converting 
each  mixture  into  a  concrete  of  the  proper  consistency  and  measuring 
the  volume  of  each  in  the  cylinder. 

That  proportion  of  sand  and  rock  which  will  give  the  smallest 
volume  will  be  the  proper  proportion  to  use. 

This  method  is  much  used  in  large  work,  and  is  very  well  adapted 
to  work  requiring  great  density  and  easy  casting  qualities.  This 
method  was  introduced  into  this  country  from  France,  and  was  first 
applied  in  this  country  by  A.  E.  Schutte  of  Warren  Bros.  Coast.  Co. 
The  method  technically  is  known  as  the  "Volumetric  Synthetic 
Method." 

(3) 

The       The  Concrete  Law  —  By  this  method,  which  is  by  far  the  most 

scientific  scientific,  the  sizing  of  particles  and  the  sizes  of  the  voids  are  taken 

grading  into  consideration.     It  will  on  a  moment's  reflection  be  evident  that  the 

of  sizes  mere  percent  of  voids  will  not  be  sufficient  to  determine  the  size  of 

material  that  will  fit  into  the  rock  voids.     Plate  III  will  illustrate 

the  principle.     The  "Concrete  Law"  is  not  a  theoretic  "vision,"  but 

a  law  of  the  greatest  practical  importance  and  use.     For  example, 

in  building  the  new  water  supply  for  New  York  City,  Mr.  W.  B. 

Fuller  devised  and  used  this  method  day  in  and  day  out.     By  short 

laboratory  tests  on  average  samples  of  the  sand  and  stones  in  lots 

as  delivered  on  the  work  he  determined  the  proportion   and  was 

enabled  to  construct  watertight  thin  walls  and  effect  a  saving  of  many 

thousands  of  dollars. 


GOOD  CONCRETE  41 

The  Concrete  Law  presupposes  a  knowledge  of  the  sizes  of  the 
particles  entering  into  the  make-up  of  concrete.  This  knowledge  is 
gained  from  the  mechanical  analysis  of  the  sand  and  rock.  No  at- 
tempt will  be  made  here  to  go  into  the  mathematics  by  which  the  law 
was  deduced,  but  the  proven  law  and  its  factors  will  be  stated. 

It  has  been  found  that  by  so  proportioning  the  sand  and  rock  that  Curve  of 

the  mechanical  analysis  gives  a  curve  of  definite  form  the  densest  greatest 

mixture  is  obtained.     This  curve  is  called  the  curve  of  greatest  den-  density 
sityt  or 

"Parabola  of  Maximum  Density": — Plate  IV  shows  the  shape 
of  the  curve  of  greatest  density  for  each  size  of  material. 

It  will  be  seen  on  inspection  that  the  curves  vary  according  to  the 
size  of  the  "largest  stones." 

It  is  the  grading  down  from  the  largest  size  to  the  smallest  in  such 
a  manner  that  the  smallest  particles  fit  into  the  voids  between  the 
larger  ones. 

Table  VIII  gives  the  quantities  by  weight  necessary  for  each  size 
when  the  "largest  stone"  is  2^",  2",  1  '/$",  1",  %"  and  Y2" ',  re- 
spectively.    It  must  be  borne  in  mind  that  in  the  actual  practical  grad- 
ing the  material  will  not  always — in  fact,  seldom — proportion  exactly 
so  as  to  give  the  curves  as  regular  as  those  in  Plate  IV,  but  they  will 
approximate  them  quite  closely.     The  concrete  law  may  be  stated 
as  follows:     To  find  the  percent  of  any  size  of  aggregate  necessary    The 
for  a  concrete  of  greatest  strength  and  density:    Divide  the  diameter  concrete 
of  the  size  sought  by  the  diameter  of  the  largest  stone  in  the  aggre-   law 
gate.     Extract  the  square  root  of  the  quotient,  and  multiply  by  100. 

Expressed  as  a  formula,  the  above  will  be,  if 

D=diameter  of  largest  stone  in  aggregate 
d  =  diameter  of  size  sought 
P  =  %  of  the  size  sought 


P=  100  (Square  root  of  ^      J 


42  GOOD  CONCRETE 

The       Table  VIII  should  now  be  closely  studied.     It  will  be  seen  that 
largest  the  size  of  the  "Largest  stone"  plays  a  most  important  role.     Upon  it 
slor.e  will  depend  all  the  percentages  of  the  various  sizes  necessary  to  pro- 
duce the  densest  mass.     The  amount  of  sand  is  directly  dependent 
upon  the  size  of  the  "largest  stone."     Consider,  for  example,  an 
aggregate  whose  "largest  stone"  is  2]/2rr-     Table  VIII  on  the  line 
marked  2^/2."  will  give  the  percent  of  various  sizes  and  the  figures 
under  the  column  marked  No.  4  will  give  the  %  of  sand,  which  for 
the  rock  under  consideration  will  be  29%. 

The  amount  For  2     "  slone  the  %  of  sand  ™U  be  33.3% 

of  sand  For  '  Vl"  slone  the  %  of  sand  will  be  38.4% 

depends  on  For  '      "  stone  tne  %  of  sand  will  be  47.0% 

the  "largest  For     24"  stone  tn«  %  of  sand  will  be  54.0% 

stone"  For    Vi"  stone  the  %  of  sand  will  be  66.5% 

The  percent  of  sand  grows  larger  as  the  size  of  the  "largest  slone" 
decreases. 


GOOD  CONCRETE 


43 


.1 


3 1 

5  I 


i 


o 


S 


g 


CM 


44  GOOD  CONCRETE 


Now  as  to   the  practical   application  of  the   "Concrete  Law": 

The  reader  has,  perhaps,  looked  with  skepticism  upon  the  above 
formula  and  figures  as  too  "Theoretic"  for  a  "practical  man."  The 
so-called  "practical  man"  is  usually  devoid  of  the  theoretic  founda- 
tion of  the  principles  he  unwittingly  applies  in  his  daily  work,  and 
is  very  fond  of  hiding  this  lack  of  knowledge  behind  a  veil  of  scoffing 
at  all  things  theoretic.  Even  the  most  ignorant  cement  worker  will 
not  deny  that  the  densest  concrete  is  the  strongest  and  that  it  is  well 
to  mix  coarse  and  fine  aggregate.  In  so  doing  he  is  unconsciously 
applying  the  principle  of  the  concrete  law. 

By  making  himself  master  of  the  principle  involved  in  the  law 
the  sidewalk,  pipe  and  block  maker  will  be  enabled  to  greatly  im- 
prove the  quality  of  his  work. 

To  APPLY  THE  CONCRETE  LAW: 

7s/:  Determine  the  size  of  the  "largest  stone"  by  screening  through 
a  set  of  sieves.  For  example,  if  a  weighed  quantify  will  all  pass 
a  2"  sieve  and  remain  partly  on  a  /J/z",  then  the  "largest  stone"  is 
said  to  be  2". 

2nd:  Make  a  complete  mechanical  analysis  for  the  various  sizes 
of  the  rock  «eves  (down  to  ]/4"),  as  explained  on  page  25. 

3rd:  Compare  this  analysis  with  that  of  the  same  size  of  the 
"largest  stone"  found  in  Table  Vlll. 

4th:  Figure  the  actual  percent  of  each  size  by  subtracting  the 
successive  amounts  of  the  percent  passing  each  sieve  for  the  mechan- 
ical analysis  of  the  "curve  of  the  greatest  density." 

For  example,  if  the  "largest  stone"  is  2",  then  from  Table  VIII 
we  get  the  percent  of  each  size  as  follows: 

100.0  —  86.6  =  1 3.4%  by  weight  of  2"  size 
86.6  —  70.6  =  16.0%  by  weight  of  1|/2"  size 
70.6  —  61.2  =.  9.4%  by  weight  of  1"  size 
61.2  —  47.0  =  14.2%  by  weight  of  %"  size 
47.0  —  33.3  =•  13.7%  by  weight  of  !/2"  »ze 
And  33.3%  by  weight  will  be  sand. 


GOOD  CONCRETE 45 

Now  repeat  this  operation  for  the  mechanical  analysis  of  the  aggre- 
gate under  consideration  and  compare  the  percent  of  each  size  with 
the  corresponding  amounts  above  and  the  difference  between  the  two 
will  indicate  the  amount  to  subtract  or  add  to  each  size  to  produce 
the  densest  concrete. 

5th:  Amount  of  cement  to  use:  The  amount  of  cement  ivill 
have  to  be  such  as  to  fill  the  voids  in  the  sand  with  cement  paste  as 
explained  on  page  34. 

For  example: — If  the  "largest  stone"  is  2"  then  Table  VIII  gives  H°v>  much 
the  percent  of  sand  as  33.3  by  weight 

Find  what  volume  of  sand  this  corresponds  to  and  figure  the  amount 
of  cement  necessary  to  fill  the  voids  with  "cement  paste,"  using  Table 
VI  to  determine  the  voids.  It  must  be  borne  in  mind  that  all  the 
percentages  in  the  concrete  law  are  by  weight.  The  weights  are 
readily  converted  to  volumes  by  the  weight  per  cubic  foot  of  each  of 
the  sizes.  This  data  is  very  readily  obtained  by  the  methods  already 
enlarged  upon. 

UNITS  OF  MEASUREMENTS  IN  PROPORTIONING. 

In  proportioning  concrete  the  materials  are  not  usually  weighed.   The  sack  °f 
but  measured  by  volume. 

The  sack  of  cement  is  taken  as  a  unit  of  measurement.      For  all 

•    i  i         •   ..  i  i         r»  r        ii     measurement 

practical  purposes  its  volume  is  taken  as  I  cu.  ft.  as  it  comes  from  the 

manufacturer.  The  cement  should  not  as  a  rule  be  measured  loose. 
If  measured  loose  the  "cubic  foot"  measure  must  be  such  as  will 
contain  94  Ibs.  of  cement  The  sand  and  rock  are  measured  in 
cubic  feet  If,  for  example,  a  specified  proportion  of  1 :2 :4  is  to  be 
mixed  and  a  two-sack  batch  of  concrete  is  wanted,  then  the  cement 
will  be  2  sacks,  the  sand  2x2=4  cu.  ft.  and  2x4=8  cu.  ft.  of  rock. 
Or  two  cubic  feet  of  cement  in  12  cu.  ft.  of  aggregate. 

CONSISTENCY  OF  THE  CONCRETE  AND  MORTAR.  Hotv 

The  average  worker  in  cement  either  uses  too  much  water  or  goes  mu< 
to  the  other  extreme  and  uses  too  little.  n>a/erP 


46 GOOD  CONCRETE 

A  dry  mixture  such  as  is  used  for  pipe  and  blocks,  should  contain 
just  enough  water  to  make  it  stick  together  when  squeezed  between 
the  hands,  or  such  an  amount  that  vigorous  tamping  will  be  necessary 
to  flush  water  to  the  surface. 

In  using  a  dry  mixture  it  is  important  that  certain  precautions  be 
•bserved.  The  mortar  or  concrete  must  be  protected  from  drying 
out  before  it  is  placed  in  the  forms  and  after.  For  this  reason  dry 
mixtures  should  never  be  worked  in  the  direct  sunlight  or  in  even 

gentle  draughts.  The  work  should  be  performed  under  cover  and 
great  care  exercised  to  keep  the  moulded  work  damp  by  a  judicious 
and  adequate  application  of  water. 

Cement       Wei  Mixtures: — By  the  term  "wet"  is  not  meant  inundated.     If 
scum  too  much  water  is  used  with  cement  it  decomposes  it,  forming  a  milk- 
like  scum  called  "Laitance" 

"Laitance"  has  no  capacity  to  "set  up,"  but  dries  out  to  a  talc- 
like  substance. 

"Laitance"  always  appears  on  the  surface  of  a  drowned  concrete 
and  prevents  a  proper  bond  between  two  consecutive  layers  of  the 
concrete.  For  this  reason  if  it  is  formed  proper  provision  should 
be  made  for  draining  it  off.  A  "wet"  mixture  is  of  such  con- 
sistency that  it  cannot  be  tamped  without  quaking.  It  must  be  a 
stiff  jelly  sufficiently  mobile  to  flow  easily  without  a  segregation  of 
the  aggregate. 

Rule  for       Amount  of  Water:— No  definite  rules  can  be  laid  down  for  the 
computing  the  amount  of  water  necessary  for  a  mortar  or  concrete. 

amount        TI  j      •» 

of  voter  *  Cariy  varying  amounts  of  water  as  "moisture"  that 

must  be  taken  into  consideration. 

If  the  sand  is  perfectly  dry  then  a  convenient  rule  to  follow  to 
determine  the  approximate  amount  of  water  to  produce  the  desired 
consistency  of  the  concrete  will  be  as  follows: 

Multiply  the  parts  of  sand  by  8,  add  24  to  the  product  and  divide 
the  total  by  the  sum  of  the  parts  of  cement  and  sand. 


GOOD  CONCRETE 47 

Example:      What  amount  of  water  will  a  1  :2  mortar  need? 
2'x  8=16 
+24 

3)40 

13.3%  water  by  weight. 

That  is  13.3%  of  the  combined  weight  of  the  sand  and  cement 
will  be  the  amount  of  water  necessary.  This  will  then  reduce  to 
gallons  if  the  weight  by  sand  and  cement  to  a  batch  is  known  and 
remembering  that  1  gallon  weighs  8.4  Ibs. 

Example:  What  amount  of  water  will  be  necessary  for  a  1  :3:6 
concrete? 

3  x  8=24 
+24 


4)48 

12%  by  weight  of  the  cement,  sand 
and  rock. 

The  concrete  worker  should  make  trial  mixtures  to  determine  the 
proper  amount  of  water  to  use  for  any  size  batch  and  set  his  water 
measure  accordingly. 

It  will  be  noticed  during  the  day  that,  particularly  in  the  summer, 
the  amount  of  water  necessary  to  produce  the  same  consistency  will 
vary  from  morning  to  noon  and  from  noon  to  sundown. 

This  fact  must  be  considered  in  pouring  reinforced  concrete  work. 

EFFECT  OF  THE  CHEMICAL  COMPOSITION  OF  THE  MIXING 

WATER  UPON  THE  STRENGTH  OF  THE 

CONCRETE. 

Little  or  no  attention  is  usually  paid  to  the  nature  of  the  water 
to  be  used  in  mixing  the  concrete. 


48  _  GOOD  CONCRETE 

Effect       There  have  been  some  notable  failures  in  concrete  construction 
of  the  that  were  directly  traceable  to  the  chemical  composition  of  the  water 
mixing  water  utcd. 

,  .         All  water  contains  dissolved  salts.    It  is  the  chemical  nature  of 

these  salts  that  will  determine  the  fitness  of  any  water  for  use  in 
concrete. 

Sea  water  or  even  brackish  water  greatly  retards  the  "setting  up" 
of  a  concrete  if  used  in  mixing. 

Hard  waters  have  a  varying  effect  according  to  salts  producing 
the  hardness.  If  the  hardness  is  due  to  sulphate  of  lime  and  sul- 
phate of  magnesia,  the  water  should  not  be  used,  as  they  can  so 
retard  the  "setting  up"  as  to  allow  the  normal  evaporation  to  rob 
the  concrete  of  the  water  or  moisture  necessary  for  hardening  before 
it  can  be  combined  chemically  with  the  cement. 

Waters  from  mineral  and  hot  springs  should  be  avoided  as 
they  are  usually  highly  charged  with  salts  that  may  attack  the  con- 
crete and  greatly  impair  its  strength. 

Water  from  swamps  is  particularly  deleterious  in  its  action  upon 
the  concrete. 

Usually  stream  and  city  main  waters  are  perfectly  safe. 

The  above  is  written  to  caution  the  cement  worker  doing  work 
in  places  where  good  water  is  not  to  be  had. 

MIXING. 

The  properly  proportioned  cement  and  aggregate  is  not  yet  a 
concrete. 

Work  is       It  becomes  concrete  upon  being  thoroughly  worked  up  and  mixed 
important  with  the  necessary  amount  of  water. 


ingredient      To  3^0^^  this  ca,u  for  a  definite  expenditure  of  work   ehher 
ncretc  muscular  or  mechanical. 

We  may  then  define  concrete  as  a  mixture  of  cement,  aggregate 
and  water  plus  work- 


GOOD  CONCRETE 49 

Concrete  is  mixed  either  by  hand  or  machinery.  Machine  mixing 
is  by  far  the  best  method. 

A  leaner  mixture,  machine  mixed,  is  usually  stronger  than  a  richer 
one  mixed  by  hand. 

In  the  past  few  years  machine  concrete  mixers  have  become  highly 
perfected  so  that  today  there  are  mixers  to  fit  the  needs  of  the 
smallest  job. 

In  the  hand  mixing  of  concrete  the  measured  aggregate  must  be  Handmixing 
manipulated  on   a   water-tight  and  rigid  platform  placed  perfectly 
level. 

The  first  consideration  is  the  thorough  mixing  of  the  sand  and 
cement  in  a  dry  state,  converting  it  into  a  plastic  mortar  by  the 
proper  application  of  water,  and  then  incorporating  the  rock. 

In  the  application  of  the  water  to  the  mixed  aggregate  and  cement.  Applying 
an  excellent  opportunity  is  had  for  completely  ruining  the  concrete,  the  water 
If  the  water  is  violently  thrown  on,  the  cement  is  washed  away  from 
the  sand.      Another  very  easy  way  to  accomplish  the  same  result 
is  to  "squirt"  the  water  on  with  a  strong  stream  from  a  hose. 

Water  should  be  sprinkled  gently  on  the  aggregate  and  cement 
mixture  and  worked  into  it  by  turning  the  mass. 

A  lawn  sprinkler  nozzle  on  a  hose  will  be  found  well  adapted  to 
the  proper  application  of  the  water. 

If  buckets  are  used  the  water  should  be  gently  poured  into  a  crater 
formed  in  the  mass  and  allowed  to  absorb. 

A  good  method  of  hand-mixing  is  to  prepare  a  mortar  box  large  A  good  way 
enough  to  accommodate  the  sand  and  cement  for  a  particular  batch  to  mix  by 
of  concrete.      The  sand  and  cement  are  thoroughly  mixed  dry,  and  hand 
then  the  water  added  and  the  whole  worked  up  to  a  moderately  stiff 
mortar.     The    measured    rock   is   then   spread   out   on   the    mixing 
platform  in  a  layer  about  6"  thick,  and  on  it  is  shoveled  the  mortar 
prepared  in  the  mortar  box,  and  worked  into  it  by  turning  the  mass 


50  _  GOOD  CONCRETE 

over.      Before  placing  the  mortar  on  the  rock  the  rock  should  be 
thoroughly  drenched  with  water. 

By  this  method  an  average  of  about  2  cu.  yds.  per  ten  hours  per 
man  can  be  mixed. 

The  practice  of  mixing  the  cement  and  aggregate  together  dry 
and  then  applying  the  water  does  not  give  as  good  results  as  the 
above  method,  and  it  will  be  found  that  more  turns  are  necessary 
to  give  a  uniform  concrete. 

In  turning  the  material  the  laborer  should  acquire  the  "trick"  of 
twisting  the  shovel  as  he  dumps  it. 

About  three  turns  dry  and  three  wet  will  usually  be  sufficient  to 
give  a  good  mixture. 

Above  all  things  the  cement  grout  must  be  kept  in  the  mass  and 
not  allowed  to  lealf 


MACHINE  MIXING. 
Machine  concrete  mixers  are  of  two  general  types. 

(  1  )  Continuous  mixers,  in  which  the  cement,  aggregate  and  water 
are  charged  into  the  machine  continuously  by  automatic  proportion- 
ing devices  and  the  concrete  discharged  in  a  steady  stream. 

(2)  Batch  mixers,  in  which  the  materials  are  proportioned  out- 
side of  the  machine,  charged  into  it,  mixed  and  discharged  as 
batches. 

Continuous  mixers  are  made  in  all  sizes  from  a  portable  machine 
that  can  be  drawn  by  one  man  up  to  those  requiring  a  span  of 
horses. 

In  this  type  of  mixer  great  care  must  be  exercised  in  operating 
to  see  that  the  proportioning  mechanism  does  not  fail  to  feed  the 
material  uniformly,  otherwise  a  streaky  concrete  results. 

Batch  mixers  are  of  two  types,  the  tilting  and  stationary.  In  the 
tilting  batch  mixer  the  mixing  drum  is  tilted  to  discharge  the  con- 


GOOD  CONCRETE  51 


crete.      In  the  stationary  type  a  movable  chute  or  spoon  dips  out  the 
material. 

The  reader  is  referred  to  the  trade  literature  of  the  manufacturers 
for  a  further  description  of  each  type. 

In  using  either  type  of  the  batch  mixer,  the  sand  and  cement 
should  be  charged  into  the  drum  dry,  the  machine  allowed  to  make 
a  few  revolutions  to  mix  the  cement  and  sand,  and  then  charge 
in  the  rock  and  water.  This  will  give  the  best  mixing  possible,  and 
at  the  same  time  it  will  not  take  any  more  time  than  charging  in  the 
cement  aggregate  and  water  together. 

In  the  stationary  type  of  batch  mixer  it  will  be  well  to  call  alien- 
tion  to  a  very  imporlant  point.      The  spoon  that  dips  out  the  mate-  concrete  and 
rial  very  often  will  deliver  rock  devoid  of  grout,  and  then  the  grout  ^on>  *° 
on  discharging.      This  difficulty  is  done  away  with  if  the  discharged  avm"  l* 
concrete  is  allowed  to  fall  into  a  hopper  and  drawn  from  it  to  be 
transporled  lo  ihe  work.      This  segregation  of  the  rock  and  mortar 
is  more  likely  to  take  place  when  the  mixture  is  too  wet. 

DEPOSITING  THE  CONCRETE. 

The  size  of  the  batch  of  concrete  should  not  be  larger  than  can  Size  of 
conveniently  be  placed  before  initial  set  takes  place.  batch 

Concrete  should  be  placed  within  thirty  minutes  after  mixing. 

The  forms  must  be  properly  aligned,  wetted  and  braced  before  Placing 
the  concrete  is  deposited.  concrete 

The  deposited  concrete,  in  layers  not  exceeding  6",  is  then  com- 
pacted  by  slicing  the  mass  with  a  spade  or  slicing  tool. 

Concrete  of  the  proper  consistency  cannot  be  tamped  with  a  tamper 
as  it  will  quake. 

It  is  compacted  by  working  a  spade  or  slicing  tool  up  and  down 
in  the  mass  and  next  to  the  forms.  By  this  method  the  air  is  ex- 
pelled and  the  concrete  compacted  much  better  than  by  the  old 
method  of  using  "dry"  concrete  and  vigorously  tamping  it. 


52 GOOD  CONCRETE 

A  convenient  slicing  tool  is  made  by  riveting  a  flat  piece  of  boiler 
plate  |4"  x  3"  x  8"  to  a  piece  of  Yz"  pipe  of  convenient  length. 

For  transporting  the  concrete  from  the  place  of  mixing  to  the 
place  of  disposition  wheelbarrows  or  the  familiar  concrete  carts  are 

used.  In  wheeling  a  concrete  in  this  manner  it  will  sometimes 
happen  that  the  sand  and  rock  will  settle  and  pack  on  the  bottom  of 
the  vehicles.  This  is,  by  the  uninitiated,  often  called  "setting,"  and 
as  a  rule  is  promptly  blamed  upon  the  cement  used. 

This  occurrence  is  but  an  evidence  that  the  mixture  is  oversanded 
and  too  wet.  It  is  readily  remedied  by  proportioning  the  mixture 
by  the  "cylinder  method"  (page  39).  The  densest  mixture  de- 
termined by  this  method  will  not  pack  or  settle  and  will  give  a  free 
casting  concrete. 

In  pouring  or  casting  work  that  is  to  come  up  exactly  to  an 
established  level,  as  for  instance,  a  column,  the  shrinkage  which  takes 
place  in  setting  up  must  be  taken  into  consideration.  The  work 
should  be  allowed  to  stand  for  a  few  hours  to  let  the  settlement  take 
place,  before  it  is  brought  up  to  the  prescribed  level. 

This  is  of  particular  importance  in  reinforced  concrete  construc- 
tion where  a  girder  is  to  be  cast  directly  onto  the  column. 

Bonding  one  Jap's  work  *>*&  another: — The  concrete  should 
always  be  run  in  horizontal  courses,  and  not  in  vertical  ones,  and 
allowed  to  slope  off  at  the  ends.  Appearance  alone  would  condemn 
this  procedure. 

How  to        In  stopping  a  day's  work  the  first  consideration  should  be  to  leave 

slop  a  the  upper  surface  of  the  concrete  in  such  shape  as  to  facilitate  the 

Jap's  work  bonding  of  the  next  day's  work  to  it     The  laitance  and  scum  that 

works  to  the  top  should  be  drained  off  and  the  surface  roughened 

and  covered  with  wet  sacks  or  sand.      Before  starting  the  next  day's 

work  this  surface  should  receive  a  thin  coat  of  sand  and  cement 

mortar  and  scrubbed  in  with  a  stiff  broom  or  brush. 


CHAPTER  IV. 


THE  PROPERTIES  OF  CONCRETE. 

The  properly  prepared  cement  and  aggregate,  when  converted  into 
a  more  or  less  plastic  mass  by  the  addition  of  water  and  an  expendi- 
ture of  work,  will  after  a  short  time  harden  into  a  stone-like  mass. 
This  hardened  mass  (concrete)  possesses  characteristic  properties 
which  distinguish  it  from  other  materials ;  just  as  a  block  of  wood  has 
properties  which  distinguish  it  from  a  block  of  iron  or  stone. 

A  proper  understanding  of  the  properties  of  any  material  is 
essential  to  its  intelligent  use. 

Concrete  does  not  attain  its  full  strength  as  soon  as  it  is  made.   Strength 
The  process  of  hardening  is  one  that  takes  years.      For  practical 
purposes  the  vital  point  of  course  is  to  know  how  soon  it  will  be 
strong  enough  to  take  the  strain  for  which  it  is  intended. 

The   rapidity  with   which  the   early  hardening  takes   place  will  Hardening 
depend  principally  upon  the  temperature.      Concrete  hardens  much   depends  on 
slower  in  cold  than  in  warm  weather.      The  temperature      of  the   the  weather 
aggregate,  mixing  water  and  the  air  will  control  the  early  stages  of 
hardening  or  "setting  up."      In  cold  weather  the  aggregate  is  chilled, 
the  water  and  air  are  cold  and  the  concrete  "sets  up"  very  slowly, 
making  it  necessary  to  leave  the  forms  on  the  work  a  much  longer 
time  than  in  warm  weather. 


54 


GOOD  CONCRETE 


So  marked  is  the  influence  of  temperature  that  it  becomes  uneco- 
nomical to  attempt  to  lay  or  pour  concrete  when  the  temperature  is 
lower  than  40  F.,  unless  the  aggregate  and  water  are  heated.     Con- 
Frozen  crete  should  not  be  laid  or  poured  in   freezing  weather.      Frozen 
concrete  green  concrete  will  not  set  up  because  the   cement  cannot  get  the 
necessary  water  for  hardening  when  it  (the  water)  is  solid.     Frozen 
concrete  will  "set  up"  upon  "thawing  out"  and  attain  a  fair  degree 
of  strength,  but  will  never  withstand  constant  exposure  to  water     The 
surface  of  the  concrete  will,  however,  blister  or  flake  off  under  the 
action  of  the  frost.      This  effect,  however,  is  only  superficial. 

Effect  of       Low  temperature  affects  only  the  early  strength  of  a  mortar  or 

cold  on  concrete.      When  once  the  hardening  has  begun,  the  progress  is  but 

strength  slightly   influenced   by   temperature.      It   is   therefore    important   to 

of  concrete  have  favorable  conditions  of  temperature  at  the  time  of  making.    The 

prevailing  temperature  at  the  time  of  making  will  control  the  time 

in  which  the  forms  can  safely  be  removed  from  the  mass. 


TABLE  IX. 

COMPRESSIVE  STRENGTH  OF  AVERAGE  CONCRETE  MADE  AT 
U.  S.  ARSENAL,  WATERTOWN,  NEW  YORK. 


Prop. 

AGE 

7  days 

1   month 

3  months 

6  months 

1:2:4 
1:3:6 

1565 
1311 

2399 
2164 

2896 
2522 

3826 
3088 

CHANGES  IN  VOLUME. 

Expansion  Hardened  concrete,  like  metal,  expands  and  contracts  with  a  rise 
and  fall  of  temperature.  Careful  experiments  have  been  made  to 
determine  the  amount  of  this  change  of  volume.  It  has  been  estab- 
lished that  average  concrete  expands  and  contracts  almost  exactly  as 
much  by  a  change  in  temperature  as  does  iron  and  steel. 


GOOD  CONCRETE 


For  every  1  °  F.  rise  in  temperature,  concrete  will  expand  .000006 
times  its  length.  So  that,  for  example,  a  wall  100  feet  long  will 
expand  with  a  rise  in  temperature  of  50°  F: — 

100  x  (.000006  x  50')=0.03'=0.36" 

It  is  this  expansion  by  heat  that  is  primarily  responsible  for  the 
familiar  cracking  of  concrete  work. 

Aside  from  the  change  of  volume  due  to  temperature  there  are  Shrinkage 
other  changes  that  are  not  so  well  recognized.  That  neat  cement, 
sand-cement,  mortar,  concrete  as  well  as  most  structural  stones  (in- 
cluding brick)  show  a  change  of  volume  when  stored  in  air  or  in 
water,  is  a  fact  that  is  now  well  established  by  many  careful  re- 
searches. Generally  a  mortar  or  concrete  will  show  a  shrinkage  in 
air  and  an  expansion  in  water. 

This  change  of  volume  is  greatest  during  the  early  hardening,  and 
grows  less  with  age. 

The  degree  of  the  change  is  proportional  to  the  amount  of  cement 
in  the  mass.  Neat  cement  changes  more  than  a  1  :3  mortar  and  a 
1:2:4  concrete  less  than  a  1:3  mortar. 

TABLE  X. 

SHOWING  NORMAL  CHANGES  IN  VOLUME.  INCHES  PER  100  FT. 
OF  LENGTH. 


Mixture 

Shrinkage  in  Air 

Expansion  in  Water 

1  month 

Iyer 

2  years 

1  month 

1  year 

2  years 

Neat  Cement 

1.9" 

2.4" 

2.7" 

0.98" 

1.75" 

1.82" 

1:3  Mortar 

0.492" 

0.63" 

.78" 

0.618" 

0.276" 

0.288" 

1:2:4  Concrete 

0.312" 

0.300" 

0.312" 

0.104" 

0.110" 

0.107" 

Table  X.  is  based  upon  the  experiments  of  Considiere  and 
Schumann.  This  shrinkage  in  air  and  expansion  in  water  must  not 
be  confused  with  the  changes  in  volume  due  to  temperature.  The 
figures  in  Table  X.  are  based  on  a  constant  unchanging  temperature. 


56  GOOD  CONCRETE 

In  building  a  structure  of  concrete  this  change  of  volume  must  be 
taken  into  consideration  and  provided  for. 

It  is  a  common  observation  that  plastered  surfaces,  sidewalks  and 
walls  will  crack  when  only  a  few  days  old,  and  again  old  work 
will  badly  craze  upon  the  surface.  These  are  but  manifestations  ot 
shrinkage. 

In  a  continuous  piece  of  work  (monolithic)  this  shrinkage  in 
hardening  will  induce  strains  that  produce  cracks. 

If  the  hardening  takes  place  in  a  sheltered  place  with  uniform 
temperature  the  cracks  are  less  likely  to  occur. 

Draw  •    A  freshly  placed  mortar  or  concrete  in  strong  sunlight  and  draughts 
cracks  will  show  "Jrau?  cracks"  upon  setting  up.     These  draw  cracks  are 

due   to   shrinkage.      They   result    from   the   top    layers   of    material 

shrinking  faster  than  the  interior  of  the  mass. 

If  the  mortar  of  concrete  contains  a  great  deal  of  very  fine  sand, 
this  effect  becomes  particularly  conspicuous.  The  excess  of  water 
necessary  to  bring  a  fine  sand  up  to  a  desired  consistency,  upon 
being  expelled  in  setting  up,  leaves  the  space  it  occupied  void. 
These  voids  greatly  facilitate  the  shrinkage  and  "</ran>  cracks" 
result. 

To  insure  the  permanency  and  appearance  of  concrete  surface 
these  factors  must  be  taken  into  consideration. 

The  effect  of  shrinkage  is  less  for  dense  than  for  porous  concretes 
and  mortars. 

Rich  mixtures  shrink  rnore  than  leaner  ones. 

Crazing      The  "crazing"  of  finished  surfaces  is  a  result  of  shrinkage.     Sur- 
faces should  therefore  never  be  finished  with  neat  cement. 

Perhaps  the  most  effective  means  of  preventing  "crazing"  is  to 
use  a  mortar  containing  not  less  than  \Y2  parts  of  sand  to  1  part 
cement  and  to  not  over-trowel  the  surface. 


GOOD  CONCRETE  57 

It  is  a  well-known  fact  that  "pebble-dashed"  or  rough  finished 
surfaces  do  not  show  "craze." 

If  a  concrete  surface  is  over-troweled  the  neat  cement  is  drawn 
to  the  surface. 

In  proportioning  concrete  by  the  "volumetric  synthetic"  method 
(as  explained  on  page  39),  if  each  of  the  trial  mixtures  are  moulded 
into  cylinders  and  allowed  to  harden  the  shrinkage  of  each  mixture 
can1  very  readily  be  measured.  It  will  be  found  that  the  mixture 
giving  the  smallest  volume  (i.  e.  the  densest)  will  show  the  smallest 
shrinkage  upon  hardening. 

In  large  and  important  structures  shrinkage  becomes  an  impor- 
tant factor  and  elaborate  provision  must  be  made  to  reduce  its  effect. 

IMPERMEABILITY  OR  WATER-TIGHTNESS. 
It  is  a  common  belief  that  concrete  is  by  nature  not  watertight. 

Porous  concrete  is,  however,  but  the  result  of  the  "hit  or  miss" 
proportioning  of  the  aggregate. 

Watertightness  is  a  relative  term.  A  concrete  may  be  watertight 
for  low  or  moderate  pressures  and  freely  allow  the  passage  of  water 
for  higher  ones. 

Watertightness  depends  upon  the  density  of  the  mass,  the  con- 
sistency, the  care  with  which  the  concrete  is  placed  and  compacted 
and  upon  the  absence  of  pockets  and  shrinkage  cracks,  and  in  a 
measure  upon  the  amount  of  cement  in  the  mass.  Thin  watertight 
walls  have,  however,  been  constructed  by  scientifically  grading  the 
aggregate  according  to  the  "concrete  law." 

It  is  a  very  simple  matter  to  compute  the  density  of  a  concrete  and    Measure- 
mortar.     Density  is  the  sum  of  the  volumes  of  solid  material  con-    rnent  of 
tained  in  the  mass.     Thus  if  we  have  a  cubic  foot  of  sand  which     density 
weighs  100  Ibs.  we  know  from  Table  VI  (page  33)  that  it  contains 
39%  of  voids  or  1.00—0.39  or  0.61   cu.  ft.  of  solid  material. 


58      GOOD  CONCRETE 

How  to  NOVV  the  weight  of  any  loose  substance  divided  by  the  weight 
per  cu.  ft.  of  that  substance  in  the  solid  state  will  give  the  volume  of 
solid  material. 

Thus  for  the  sand  just  considered,  if  the  weight  per  cu.  ft.  loose  is 
divided  by  the  weight  per  cu.  ft.  solid,  i.  e. : 
100 

=0.61  will  be  the  density  or  the  volume  of  solid  material  in  1 

1 65     cu   ft.  of  loose  material. 

To  compute  the  density  of  a  concrete  proceed  as  follows: 

Wt.  of  cement   ,    Wt.  of  sand    ,  Wt.  of  rock  ,    Wt.  of  water 

193  165          f  Wt.  solid  per  cu.  ft.  f         62.3 

and  this  value  divided  by  the  volume  of  concrete  will  be  the  "density." 

Consistency       Consistency: — The  consistency  of  the  concrete  should  be  that  of 

a  stiff  jelly  that  will  "puddle"  easily. 

Placing  Placing: — The  concrete  should  be  placed  continuously  and  with- 
out interruption  and  thoroughly  compacted  by  puddling  to  remove 
all  the  air.  Large  masses  should  not  be  dumped  into  place  suddenly, 
but  the  material  should  fall  in  a  moderate  stream. 

Care  of  placing: — It  is  obvious  that  if  pockets  are  formed  or 
shrinkage  cracks  allowed  to  develop  the  mass  cannot  be  watertight. 

Generally  a  concrete  increases  in  watertightness  with  age.  Dur- 
ing the  process  of  hardening  the  crystallization  and  other  changes 
that  occur  tend  to  fill  the  voids. 

For  high  pressures  at  early  age  the  concrete  surfaces  must  be 
treated  with  some  kind  of  impervious  and  elastic  material,  such  as 
a  diaphragm  of  bituminous  material. 

Water-       Waterproofing  compounds  are  added  to  the  concrete  in  mixing. 
proofing  Their  effect  upon  the  strength  will  be  considered  elsewhere.     They 
compounds  are  as  a  general  rule  not  very  efficient  and  their  use  is  of  doubtful 
value. 


GOOD  CONCRETE  59 

Watertightness  can  be  most  cheaply  and  expeditiously  obtained 
by  properly  proportioning  the  aggregate. 

RESISTANCE  OF  HARDENED  CONCRETE  TO  CHEMICAL  IN- 
FLUENCES. 

Hardened  concrete  is  more  resistant  to  chemical  action  than  any 
of  the  building  stones.  It  will  not  weather,  under  the  chemical  action 
of  the  gases  of  the  atmosphere,  as  will  marble,  granite  or  sandstone. 

Carbonic  acid   (carbon  dioxide)  which  results  from  the  combus-    Concrete 
tion  of  organic  substances,  the  decay  of  vegetable  matter  and  the    endures 
breathing  of  plants,  animals  and  human  beings,  has  only  a  beneficial 
effect  upon  the  hardened  concrete.     Concrete  is  the  only  structural 
material  which  gains  strength  with  age. 

The  action  of  water  and  carbonic  acid  upon  marble,  granite  and 
sandstone  is  perhaps  too  well  known  to  need  mention. 

If,  however,  a  concrete  is  porous  and  freely  allows  the  percola- 
tion cf  water,  some  of  the  products  formed  during  hardening  will 
be  leached  out  and  the  concrete  will  suffer  accordingly.  If,  how- 
ever, the  concrete  is  dense  such  an  action  will  not  take  place. 

Pure  distilled  water  will  attack  the  surface  of  concrete,  as  it  has 
a  greater  solvent  action  than  ordinary  water.  This  action  has  been 
noticed  in  cisterns  for  distilled  or  rain  water.  A  thin  scum  is  formed 
on  the  surface  which  consists  of  silica  and  iron  compounds  derived 
from  the  cement.  It  was  found  that  if  this  scum  was  not  removed, 
no  further  action  took  place.  But  when  the  scum  was  periodically 
removed  the  surface  was  affected  by  the  water. 

Sewage  and  stable  drainage  are  without  effect  upon  hardened  con-    Sewage 
crete,  which  fact  makes  concrete  peculiarly  suitable  for  sewer  pipe 
and  drainage  systems. 

Ail    acids    attack   concrete,    as    do   soured   milk   and    fermenting   Acids 
liquids. 


60 GOOD  CONCRETE 

Concrete  intended  for  use  where  it  will  be  subjected  to  the  action 
of  such  substances  should  be  coated  with  asphalt. 

All  sulphate  salts  will  after  a  longer  or  shorter  time  produce  dis- 
integration of  porous  concrete,  if  left  in  contact  with  it. 

Magnesium  salts  are  particularly  active  in  attacking  such  con- 
crete. All  other  salts  (chloride,  carbonate,  etc.,  etc.)  are  without 
effect  upon  the  hardened  concrete. 

Oils  Light  vegetable  oils  attack  concrete.  Mineral  oils  do  not.  Con- 
crete tanks  for  oil  storage  have  proven  themselves  well  adapted  to 
the  purpose  in  the  California  oil  fields. 

Recently  it  has  been  discovered  that  in  certain  portions  of  the 
arid  west,  concrete  in  contact  with  certain  soils  has  after  a  few  years 
disintegrated.  This  action  has  been  attributed  to  the  magnesium 
and  sodium  sulphate  present  in  the  soil. 

In  the  cases  observed  it  has  been  established  that  the  porosity 
of  the  concrete  has  absorbed  the  salts,  which  have  reacted  on  the 
interior  of  the  mass,  forming  compounds  which  upon  crystallization 
expanded  in  volume,  thus  tearing  the  concrete  to  pieces. 

The  localities  in  which  sufficient  of  these  salts  exist  in  the  soil 
are  very  limited,  being  confined  to  the  several  small  areas  on  the 
eastern  slope  of  the  Rocky  mountains.  Terra  cotta  pipes  are  also 
attacked  under  these  conditions. 

Remedy       The  obvious  remedy  for  the  evil  is  to  make  the  concrete  so  dense 
as  to  make  it  incapable  of  absorbing  the  salts. 

Behavior  of  Concrete  Towards  Metals: — Iron  and  steel  imbedded 
in  concrete  are  permanently  preserved.  Recently  some  very  old 
foundations  for  gun  carriages  were  removed  by  the  U.  S.  A.  on 
the  coast.  Anchor  bolts  of  iron  which  had  been  in  place  for  forty 
years  were  found  to  be  in  a  perfect  state  of  preservation.  In  fact, 
the  surface  next  to  the  concrete  was  found  to  be  as  bright  as  if  it 
had  been  burnished. 


GOOD  CONCRETE 61 

The  preservative  action  of  cement  on  iron  is  now  so  well  known  Steel  and 
that  mixed  with  linseed  oil  it  is  used  as  a  paint  for  iron.     Concrete  iron 
attacks  and  destroys  lead  and  zinc.     These  metals  should  therefore 
receive  a  coating  of  asphalt  when  they  come  in  contact  with  con- 
crete.     This  is  particularly  important  in  plumbing  fixtures  and  in  Lead  and 
telegraph  and  telephone  cables,  covered  with  lead,  which  are  very  zinc 
often  placed  in  contact  with  concrete. 

THE  EFFECT  OF  SEA  WATER  UPON  HARDENED  CONCRETE. 

The  effect  of  sea  water  upon  hardened  concrete  is  a  matter  which 
has  provoked  much  discussion  in  the  technical  world,  without, 
however,  producing  any  unanimity.  There  have  been,  it  is  true, 
some  notable  failures  of  concrete  structures  in  sea  water,  but  these 
have  been  by  so  far  in  the  minority  as  compared  to  the  total  number 
of  structures  built  that  their  percentage  is  negligible.  We  can,  with 
perfect  justice,  ask  what  were  the  causes  contributing  to  these  fail- 
ures. Were  they  due  to  an  inherent  general  property  of  cement  to 
disintegrate,  or  were  they  due  to  faulty  cement  or  to  faulty  aggregate, 
or,  finally,  to  the  method  of  placing  the  concrete  in  this  environment? 

There  are  two  general  methods  of  placing  concrete  in  sea  water. 
The  one  consists  of  depositing  the  material  through  a  tube  called  a 
tromie,  and  the  other  consists  of  moulding  the  structural  members 
on  land,  allowing  them  to  harden  in  air  and  then  placing  them  into 
their  final  position  in  the  sea.  It  can  be  said  generally  that  all  of 
the  failures  that  have  taken  place  in  concrete  structures  in  sea  water 
have  been  in  those  constructed  by  placing  tha  fresh  concrete  directly 
into  the  sea. 

The  action  of  sea  water  on  concrete  is  attributed  to  the  presence 
of  magnesium  sulphate  in  the  sea  water,  which  forms  with  the  lime 
and  alumina  of  the  cement  a  double  salt  of  sulphuric  acid,  alumina 
and  lime.  This  salt,  called  by  Michaelis  "sulpho  aluminate  of  lime," 
on  crystallizing  undergoes  a  great  increase  in  volume,  and  the  ex- 
pansive action  resulting  from  this  change  is  sufficient  to  destroy  the 
cohesion  of  any  mass  in  which  it  might  be  formed.  The  action  of 


62 GOOD  CONCRETE 

this  particular  salt,  and  the  possibility  of  its  formation,  can  be  ques- 
tioned, but  it  can  be  said,  in  view  of  all  the  recent  work  done  in 
Europe  and  by  the  Bureau  of  Standards  of  the  United  States,  that 
the  infiltration  and  crystallization  of  any  salt  on  the  interior  of  the 
concrete  mass  can  produce,  by  purely  mechanical  means — i.  e.,  ex- 
pansion— a  disintegration  of  the  mass.  This  effect  is  by  no  means 
confined  to  concrete  alone.  It  holds  generally  for  all  natural  stones 
and  brick,  terra  cotta,  etc.,  etc. — in  fact,  in  any  mass  which  is  at  all 
porous,  and  which  will  allow  a  growth  of  crystals  in  its  interstices, 
we  may  expect  disintegration  to  take  place  from  the  expansive  force 
exerted  during  crystallization.  This  phenomena  is  very  well  illus- 
trated by  the  expansive  force  of  water  freezing.  For  instance,  we 
know  that  water  in  freezing  will  crack  a  boiler  containing  it.  The 
ancients  used  this  method  of  quarrying  their  rock.  They  would 
fill  a  crevasse  full  of  water  and  allow  it  to  freeze. 

REMEDIES  PROPOSED  TO  IMPROVE  PORTLAND  CEMENT  FOR  USE 
IN  SEA  WATER. 

In  view  of  all  the  authoritative  tests  that  have  been  conducted  in 
Europe  and  the  United  States  during  the  last  ten  years,  we  may 
safely  state  that  Portland  Cement,  by  itself,  needs  not  to  be  im- 
proved for  use  in  sea  water.  The  improvement  must  take  place  en- 
tirely in  the  making  of  the  concrete.  In  short,  it  is  not  a  question  of 
better  cement,  but  of  better  concrete.  Perhaps  the  most  comprehen- 
sive series  of  tests  upon  the  action  of  sea  water  upon  concrete  are 
those  instituted  by  the  Scandinavian  Association  of  Portland  Cement 
Manufacturers,  co-operating  with  the  Harbor  authorities.  These 
tests  are  entitled  to  careful  consideration,  inasmuch  as  they  were 
carried  out  on  a  large  scale  under  very  severe  conditions. 

The  test  pieces  consisted  of  large  blocks  two  feet  by  four  feet 
exposed  to  the  rise  and  fall  of  the  tide,  frost  and  atmospheric  influ- 
ences at  a  number  of  localities  on  the  Baltic  Sea  and  the  coast  of 
Jutland.  The  result  of  the  ten  years'  tests  have  just  recently  become 
available.  These  tests  were  made  with  Portland  Cement  and  with 


GOOD  CONCRETE  63 

Portland  Cement  with  additions  of  trass,  infusorial  earth,  santorian 
earth,  puzzolane,  slag  and  fine  sand,  mixed  and  ground  with  the 
cement.  The  conclusions  so  far  as  they  are  possible  to  be  drawn 
from  the  ten  years'  exposure  may  be  summarized  as  follows: 

Much  depends  upon  the  compactness  of  the  mortar.  A  loose 
mortar,  by  allowing  salts  to  penetrate  to  the  interior  of  the  mass,  is 
rapidly  disintegrated.  A  rich  mortar  must  be  used.  A  mortar  con- 
sisting one  part  of  cement  to  three  parts  sand  is  not  rich  enough,  as 
the  majority  of  the  one  to  three  mortars  disintegrated,  while  the 
one  to  two  mortars  did  not.  Any  good  Portland  Cement  not  exces- 
sively high  in  alumina  appears  to  be  suitable  for  sea  construction. 

The  main  agency  of  destruction  is  not  chemical,  but  is  due  to  the 
alternate  saturation,  drying,  freezing,  etc.  The  destruction  takes 
place  sometimes  by  cracking,  sometimes  by  scaling  and  sometimes 
by  softening.  The  addition  of  finely  ground  silicious  material  is  of 
doubtful  value.  The  addition  of  an  infusorial  earth  gave  very  in- 
ferior results. 

The  destructive  action  of  the  sea  being  mainly  physical  and  me- 
chanical and  not  chemical,  tests  by  mere  immersion  in  still  sea  water 
are  of  very  little  value  in  determining  the  behavior  of  a  concrete  in 
massive  engineering  work.  A  mixture  which  disintegrates  under  these 
tests  is  certainly  useless,  but  a  mixture  which  passes  this  test  may 
disintegrate  under  the  more  stringent  conditions  of  practical  usage. 
As  long  a  period  as  practical  should  be  allowed  for  the  hardening 
of  the  concrete  in  air  before  placing  in  the  sea. 

From  the  many  successful  structures  that  are  today  resisting  the 
action  of  sea  water,  coupled  with  exhaustive  researches  made  into  the 
effect  of  sea  water  upon  concrete,  there  seems  to  be  no  room  for  a 
reasonable  doubt  that  the  success  of  concrete  in  sea  water  is  de- 
pendent principally  upon  better  concrete,  rather  than  any  modifica- 
tion of  the  chemical  composition  of  the  cement  to  be  used. 


64  GOOD  CONCRETE 

SUMMARY  OF  TEST  ON  EFFECT  OF  ALKALI  AND  SEA  WATER 
ON  CONCRETE. 

The  United  States  Bureau  of  Standards  has  within  the  last  three 
and  a  half  years  investigated  the  effect  of  alkali  and  sea  water  on 
concrete.  The  whole  matter  has  been  summed  up  in  Technologic 
Paper  No.  1 2  of  the  Bureau  of  Standards,  and  below  is  given  a  com- 
plete verbatim  summary  of  the  result  of  these  investigations: 

"The  conclusions  must  be  limited  by  the  scope  of  this  investiga- 
tion, and  since  the  physical  tests  reported  cover  a  period  of  exposure 
not  exceeding  3J/2  years  the  conclusion  should  be  considered  as  some- 
what tentative. 

1.  Portland  cement  mortar  or  concrete,  if  porous,  can  be  disin- 
tegrated by  the  mechanical  forces  exerted  by  the  crystallization  of 
almost  any  salt  in  its  pores,  if  a  sufficient  amount  of  it  is  permitted 
to  accumulate  and  a  rapid  formation  of  crystals  is  brought  about  by 
drying;  and  as  larger  crystals  are  formed  by  slow  crystallization, 
there  would  be  obtained  the  same  results  on  a  larger  scale,  but  in 
greater  time  if  slow  drying  were  had.    Porous  stone,  brick  ^nd  other 

structural  materials  are  disintegrated  in  the  same  manner.  There- 
fore in  alkali  regions  where  a  concentration  of  salts  is  possible  a  dense 
non-porous  surface  is  essential. 

2.  While  in  the  laboratory  a  hydraulic  cement  is  readily  decom- 
posed if  intimately  exposed  to  the  chemical  action  of  various  sulphate 
and  chloride  solutions,  field  inspection  indicates  that  in  service  these 
reactions  are  much  retarded,  if  not  entirely  suspended,  in  most  cases, 
due  probably  to  the  carbonization  of  the  lime  of  the  cement  near  the 
surface  or  the  formation  of  an  impervious  skin  or  protective  coating 
by  saline  deposits. 

3.  Properly  made  Portland  cement  concrete,  when  totally  im- 
mersed, is  apparently  not  subject  to  decomposition  by  the  chemical 
action  of  sea  water. 

4.  While  these  tests  indicated  that   Portland  cement  concrete 
exposed  between  tides  resisted  chemical  decomposition  as  satisfactorily 


THE  EFFECT  OF  EXPANSION  AND  SHRINKAGE  ON  SANDSTONE. 

The  spawling  of  the  outer  film  is  caused  by  the  alternate  wetting  and 
drying  of  the  surface  producing  expansion  and  shrinkage,  which  together 
with  the  expansion  ana  contraction  due  to  changes  in  temperature  has 
torn  the  surface  layer  of  stone  from  the  main  body. 

These  same  causes  grind  and  crush  the  mortar  pointing  of  the  hori- 
zontal and  vertical  joints. 


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EFFECT  OF  EXPANSION  AND  SHRINKAGE  IN  CONCRETE  AND 
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EFFECT  OF  EXPANSION  IN  A  CONCRETE  WALL. 


EFFECT  OF  SHRINKAGE  IN  A  CONCRETE  RUBBLE  WALL. 


GOOD  CONCRETE 65 

as  the  totally  immersed  concrete,  it  is  felt  that  actual  service  condi- 
tions were  not  reproduced,  and  therefore  further  investigation  is  de- 
sirable. 

5.  It  is  not  yet  possible  to  state  whether  the  resistance  of  cements 
to  chemical  disintegration  by  sea  water  is  due  to  the  superficial  forma- 
tion of  an  impervious  skin  or  coating,  which  is  subsequently  assisted 
by  the  deposition  of  shells  and  moss  forming  a  protective  coating,  or 
by  the  chemical  reaction  of  the  sea  salts  with  the  cement  forming  a 
more  stable  compound  without  disintegration  of  the  concrete,  or  by 
a  combination  of  both  of  these  phenomena. 

6.  Marine  construction,  in  so  far  as  the  concrete  placed  below 
the  surface  of  the  water  is  concerned,  would  appear  to  be  a  problem 
of  method  rather  than  materials,  as  the  concrete  sets  and  permanently 
hardens  as  satisfactorily  in  sea  water  as  in  fresh  water  or  in  the 
atmosphere,  if  it  can  be  placed  in  the  forms  without  undue  exposure 
to  the  sea  water  while  being  deposited. 

7.  Natural,   slag   and  other  special  cements   tested  in  concrete 
mixtures  showed  normal  increase  in  strength  with  age  both  in  sea 
water  and  in  fresh  water. 

8.  In  the  form  of  neat  briquettes  most  of  the  Portland  cements 
of  high  iron  content,  several  of  the  cements  of  high  or  normal  alumina 
content  and  one  special  slag  cement  did  not  show  any  marked  differ- 
ence in  tensile  strength  whether  exposed  to  fresh  or  sea  water  for  all 
periods  up  to  two  years.     Other  cements  of  various  compositions 
showed  signs  of  disintegration  after  a  few  weeks. 

9.  All  cements  resisted  disintegration  in  sea  water  better  in  mor- 
tar mixtures  than  in  the  form  of  neat  briquettes.     In  most  cases  the 
mortar  briquettes  had  normal  strength  up  to  two  years'  exposure. 

10.  The  physical  qualities  of  the  cement,  which  depend  essen- 
tially upon  the  method  of  manufacture,  would  seem  to  determine  its 
resistance  to  decomposition  when  brought  into  intimate  contact  with 
the  sulphate  and  chloride  solutions. 


GOOD  CONCRETE 

- 

1 1 .  Contrary  to  the  opinion  of  many,  there  is  no  apparent  rela- 
tion between  the  chemical  composition  of  a  cement  and  the  rapidity 
with  which  it  reacts  with  sea  water  when  brought  into  intimate  contact. 

1 2.  Tricalcium-sulpho-aluminate  could  not  be  formed,  and  there- 
fore disintegration  could  not  result  from  this  cause. 

13.  In  the  presence  of  sea   water  or  similar  sulphate-chloride 
solutions: 

(a)  The  most  soluble  element  of  the  cement  is  the  lime.      If 
the  lime  of  the  cement  is  carbonated  it  is  practically  insoluble. 

(b)  The  quantity  of  alumina,  iron  or  silica  present  in  ihe  cement 
does  not  affect  its  solubility. 

(c)  The  magnesia  present  in  the  cement  is  practically  inert. 

(d)  The  quantity  of  SOs  present  in  the  cement  up  to   1.75% 
does  not  affect  its  solubility,  but  a  variation  in  the  quantity  present 
may  affect  its  stability  by  affecting  its  rate  of  hardening. 

14.  The  change  which  takes  place  in  sea  water  when  brought 
into  intimate  contact  with  the  cement  is  as  follows: 

(a)  The  magnesia  is  precipitated  from  the  sea  water  in  direct 
proportion  to  the  solubility  of  the  lime  of  the  cement. 

(b)  The  sulphates  are  the  most  active  constituents  of  the  sea 
water  and  are  taken  up  by  the  cement.     Their  action  is  accelerated 
in  the  presence  of  chlorides.      No  definite  sulphate  compound  was 
established. 

(c)  The  quantity  of  chlorine  and  sodium  taken  up  by  the  cement 
is  so  small  that  no  statement  can  be  made  as  to  the  existence  of  any 
definite  chloride  or  sodium  compound  formed  with  the  cement. 

15.  The  SOs  added  to  a  cement  in  the  plaster  to  regulate  the 
time  of  set  is  chemically  fixed  so  that  it  will  not  go  into  solution  when 
the  cement  is  brought  into  intimate  contact  with  distilled  water. 

16.  Metal  reinforcement  is  not  subject  to  corrosion  if  embedded 
to  a  depth  of  2  in.  or  more  from  the  surface  of  well-made  concrete." 


GOOD  CONCRETE 


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SIDEWALKS 


CHAPTER  V. 


PORTLAND  CEMENT  SIDEWALKS. 

The  use  of  Portland  cement  for  sidewalk  construction  has  become  Cement 
so  universal  that  even  the  smallest  hamlet  in  the  most  remote  section  sidewalks 
of  the  country  has  its  sidewalks  constructed  therefrom.     A  cement  are 
sidewalk  if  properly  constructed  is  a  permanent  improvement  and  permanent 
one  that  adds  materially  to  the  comfort  of  the  pedestrians  and  to  the 
beauty  of  the  community. 

The   proper   construction   of   cement   sidewalks   is   not   a   matter  t/m£,-//ed 
that  can  be  entrusted  to  unskilled  and  raw  labor.     It  is  an  art,  and  /afcor  noi 
as  such  requires  a  thorough  understanding  of  the  materials  of  con-  usej 
struction  and  their  properties.     There  are  so  many  factors  upon  which 
the  success  and  permanence  of  sidewalks  depend  that  their  proper 
construction  is  not  as  simple  a  matter  as  may  appear. 

In  massive  concrete  constructions,  such  as  foundations,  any  defects 
that  might  develop  are  not  visible  to  the  eye.  The  mistakes  of  the 
constructor  are  buried.  But  in  a  sidewalk  any  errors  of  commission 
or  omission  are  very  noticeable  and  bear  mute  but  eloquent  testimony 
against  their  maker. 

As  in  any  building  operation,  a  sidewalk  will  need  a  good  and  Good 
properly  prepared  foundation.     A  good  superstructure  upon  a  poor  foundation 
foundation  is  as  much  a  failure  as  a  poor  superstructure  upon  a  good  necessary 
foundation. 


74 


GOOD  CONCRETE 


"o 

I 


c/) 


>    g 

«u  U 


I 


GOOD  CONCRETE 75 

PREPARATION  OF  THE  FOUNDATION: 

The  foundation  must  be  so  prepared  that  it  will  not  shrink  away  Foundation 
from  the  concrete  base.  All  roots  and  organic  matter  should  be 
removed  and  the  foundation  excavated  to  a  depth  corresponding  to 
the  total  thickness  of  the  slab.  In  ordinary  firm  soils  this  is  readily 
accomplished.  Sand  is  an  excellent  foundation  if  it  is  confined 
laterally  so  that  it  cannot  move  out  from  under  the  concrete  base. 
The  foundation,  or  sub-base,  must  be  made  firm  by  wetting  and 
tamping  and  must  be  wet  at  the  time  the  concrete  is  placed  upon  it. 
On  a  sand  foundation  too  much  water  is  objectionable,  in  as  much  as 
a  sand  super-saturated  with  water  will  shrink  away  from  the  concrete 
upon  drying.  The  sand  sub-base  should,  therefore,  be  just  saturated 
with  water,  just  enough  to  make  it  easy  to  compact  by  ramming. 
Fig.  3  shows  the  correct  and  incorrect  method  of  laying  a  side  walk 
on  a  sand  fill. 

The  most  troublesome  soil  the  contractor  has  to  contend  with  is   Adobe 
the  adobe  of  Central  and  Southern  California.     Even  the  most  casual   soils 
observer  knows  that  adobe  "cracks  up"  in  summer,  and  closes  up  in 
winter.       Adobe  absorbs  water,  which  shoves  its  grains  apart.     Upon 
drying  out  a  shrinkage  takes  place  that  opens  up  the  familiar  adobe 
cracks.     As  the  material  further  dries  out  it  slakes  and  falls  to  a  more 
or  less  granular  mass.     This  shrinkage  is  accompanied  by  a  force   Adobe 
sufficient  in  magnitude  to  tear  apart  a  sidewalk  resting  upon  it ;  in  fact   cracks 
adobe  has  been  known  to  crack  and  tear  apart  bodily  a  heavy  masonry 
wall.     This  shrinkage  extends  to  a  depth  of  from  4"  to  8".     If  the 
dry  adobe  is  tamped  into  place  and  kept  dry,  then  no  shrinkage  can 
take  place.     If  the  dry  adobe  is  pulverized  and  mixed  with  sand  in  the   Hom>  to 
proportion  of  /:/,  moistened  and  tamped  into  place,  it  will  make  a   treat  adobe 
very    serviceable    sub-base    for    a    sidewalk.       Fig.    2    shows    the   for  a 
details  of  these  methods.  inundation 

In  preparing  a  sub-base  in  adobe  either  of  two  methods  can  be 
used  to  insure  the  permanency  of  the  work.  ( 1  )  The  adobe  is  broken 
up  into  material  not  much  coarser  than  pea  size,  is  slightly  moistened 
and  thoroughly  tamped;  upon  this  a  layer  of  from  1"  to  2"  of  damp 


76 


GOOD  CONCRETE 


Foundation  on  Filled  Ground 


Foundation  on  Ordinary  Ground 


Surface 


c  &  d     Foundations  on  Adobe  Soil 


Fig.  2. 


GOOD  CONCRETE 


77 


Foundations  on  Sand  Fills  (Shallow  Fills) 


Wooden  bulkhead  confining  a  sand  fill.     Here  the  life  of  the  sidewalk 
is  limited  by  the  life  of  the  bulkhead. 


VI- 


b.     The  proper  method  of  confining  a  sand  fill.      This  is  a 
permanent  type  of  construction. 


Fig.  3. 


78 


GOOD  CONCRETE 


sand  or  shale  is  tamped  and  is  kept  moist  until  the  cement  base  is 
deposited.  (2)  By  making  a  mortar,  as  above  mentioned,  of  1  part 
crushed  or  pulverized  adobe  to  1  part  sand,  and  working  it  with 
just  enough  water  to  consolidate  it.  This  mortar  can  very  con- 
veniently be  prepared  in  a  concrete  mixer  (which  is  to  be  thoroughly 
cleaned  after  the  operation).  Upon  the  adobe-sand  sub-base  a  thin 
layer  of  damp  sand  is  spread  before  the  concrete  base  is  placed 
upon  it. 


FOUNDATION  ON  FILLS. 

Foundation         In  building  a  sidewalk  on  a  fill,  great  care  must  be  exercised  to  see 
on    that  the  fill  has  completely  settled.     A  newly  made  fill  will  shrink 
fills    about  15%  in  volume  upon  standing.     On  fills  that  have  been  made 
and  left  to  settle  through  one  rainy  season,  the  sidewalk  may  safely 
be  constructed  without  any  further  compacting,  apart  from  the  tamp- 
ing of  the  sub-base  grade.     If,  however,  the  fill  is  made  at  about  the 
time  the  sidewalk  is  to  be  constructed,  then  careful  soaking  with  water 
Side    and  tamping  will  be  necessary.      The  side  slopes  of  the   fill  must 
slope    conform  with  the  natural  slope  at  which  the  material  will  stand  (angle 
of  fills    of  repose  of  the  material).     The  material  must  be  deposited  in  layers 
not  exceeding  6"  in  depth,  thoroughly  wetted  and  compacted.      The 
top  of  the  fill  should  be  at  least  2"  wider  than  the  finished  sidewalk 
is  to  be. 

Drainage        The  slopes  of  the  embankment  or  fill  should  be  sodded  or  sown  to 

on  fills    grass ;  the  mat  thus  produced  will  prevent  the  fill  being  washed  by  the 

rain.     If  the  fill  cr.osses  the  natural  drainage,  drains  must  be  provided 

to  allow  the  safe  passage  of  the  water  through  the  fill  and  prevent 

the  water  damming  up  on  one  side  of  it. 

Side  slope        The  sub-base  or  foundation  should  slope  slightly  toward  the  curb, 
of  sidewalk   to  facilitate  drainage.     One-fourth  (|4)  inch  per  foot  will  be  suffi- 
cient for  this  purpose. 


GOOD  CONCRETE  79 

FACTORS  TO  BE  CONSIDERED  IN  THE  CONSTRUCTION  OF 
SIDEWALK. 

Fig.    1    shows   the   various   parts   of   which   a   sidewalk   is   com-  Factors 
posed,   consisting  of  a   sub-base  or   foundation,   a   slab  of  concrete  to  be 
called  the  base,  and  a  top  coat  or  wearing  surface.     The  require-  considered 
ments   for  the   sub-base  have  already  been  considered.      The  base  in  the 
and  top,  which  are  composed  of  concrete  and  mortar,  will  have  to  construction 
be  constructed  in  accordance  with  definite  rules  based  on  the  physi-  of  sidewalk 
cal  properties  of  concrete  and  mortar. 

On  pages  55  and  56  the  question  of  a  change  in  volume  of  the 
concrete  and  mortar  was  considered  at  length.  The  reader  is  referred 
to  it  and  advised  to  carefully  study  the  matter. 

The  change  in  volume  resulting  from  a  change  in  temperature  and  Changes 
that   resulting   from  the  natural  shrinkage   are    factors  of  vital  im-  in  volume 
portance  in  the  construction  of  sidewalks.     These  changes  in  volume  irwi^e 
are   responsible   for  the  well-known   "cracks"   that  appear  in  side-  cracks 
walks,  walls,  curbs  and  other  concrete  structures.     These  cracks  con- 
stitute the  chief  annoyance  of  the  sidewalk  builder.     The  occurrence 
of  cracks  due  to  the  change  of  volume  is  not  to  be  considered  as  a 
fault  of  the  Portland  Cement,   any  more  than  the   expansion   and 
contraction  of  steel,  or  the  shrinkage  of  clay,  are  to  be  considered 
as  faults  of  these  materials. 

When  iron  first  came  into  use  it  was  not  very  long  before  the  iron  Cracks 
worker  realized  that  allowance  had  to  be  made  in  a  structure  for  can  be 
expansion   and   contraction    resulting   from   changes   in   temperature,   prevented 
The  first  clay  workers  soon  discovered  that  a  piece  of  pottery  had 
to  be  molded  considerably  larger  than  the  finished  work,  to  allow 
for  the  shrinkage  in  burning.      The  science  in  using  any   material 
consists  in  making  due  and  intelligent  allowance  for  its  physical  prop- 
erties.    Cracks  can  and  should  be  prevented  by  making  allowance 
for  expansion  and  shrinkage. 


80  GOOD  CONCRETE 


METHODS  OF  PROVIDING  FOR  EXPANSION  AND  SHRINKAGE: 

Object  of  A  sidewalk  is  divided  up  into  the  familiar  squares  by  grooved 
marking  Jjnes>  not  only  to  improve  its  appearance  but  to  mask  the  expansion 
and  shrinkage  cracks  that  will  inevitably  appear.  These  grooved 
lines  make  planes  of  weakness.  A  sidewalk  laid  without  such  mark- 
ings will  in  the  course  of  a  very  few  days  exhibit  irregular  cracks 
running  lengthwise  and  across  the  walk,  dividing  it  into  more  or 
less  square  blocks.  That  is  to  say,  nature  is  providing  a  relief  for 
the  expansion  and  shrinkage  of  the  material  that  should  properly  have 
been  provided  by  the  builder.  Nature,  however,  in  making  these 
cracks  does  not  use  a  straight  edge,  but  lets  them  follow  any  planes 
of  least  resistance,  the  result  being  a  rather  unbeautiful  effect.  The 
result  of  so  laying  a  sidewalk  is  shown  in  Plate  V. 

Marking  Is  Not  Sufficient  Provision  for  expansion  and  shrinkage. 
Many  sidewalk  specifications  make  no  provision  for  expansion,  rely- 
ing entirely  upon  the  uncertainty  of  the  cracks  following  the  marked 
Cracks  grooves  with  which  the  surface  is  blocked  off.     That  the  cracks  do 
do  not  not  always  follow  the  marking  is  evident  in  almost  any  sidewalk. 
always  Jhey  will  at  times  form  across  the  walk,  at  others  they  will  follow  the 
follow  marking  a  part  of  the  way  and  then  leave  it.     Plate  VI  shows  such 
the  marking  an  instance.      The  crack  followed  the  marking  until  it  came  to  a 
point  where  a  piece  of  rock  was  directly  under  the  mark.     It  was 
here  deflected  to  one  side,  producing  the  defect  as  shown.      Even 
when  the  cracks  form  in  the  markings  it  is  evident  that  the  expansion 
will  cause  the  blocks  to  "rise,"  as  shown  in  Plate  VIII.   The  continual 
working  at  the  point  C  and  D  will  eventually  crumble  the  edges  of 
the  break.      The  remedy  consists  in  cutting  the  whole  length  into 
separate  blocks  separated  by  a  space  sufficiently  wide  to  allow  each 
block  to  freely  expand  without  coming  in  contact  with  its  neighbor. 

This  is  most  conveniently  accomplished  by  means  of  a  wooden 
Beaver  Board  or  steel  parting  strip  placed  across  the  forms  at  definite 
intervals. 


PLATE  V. 


A    Sidewalk    Laid    Without    Any    Markings,    Showing    How    the 
Expansion  and  Shrinkage  Has  Provided  its  Own  Marking. 


&^^^ 


Cause: — Lack  of  provision  for  expansion  and  shrinkage. 
Cracks  follow  natural  planes  of  weakness. 

< pension  joints .. 


Remedy: — Divide  surface  into  blocks  and  place  expansion  joints 
at  alternate  block  divisions. 


PLATE  VI. 


View  Showing  that  Cracks  Will  Not  Always  follow  the  Marking. 


iBiir 


Showing  Cause  of  Crack  Leaving  Marking.      The  Stone  Directly 

Under  the  Mark  Deflecting  the   Crack. 
A  C 


Showing  the  Remedy:     The  joint  C-D  is  cut  through  the  base.     Joint 

made  by  placing  a  !/g"  steel  parting  strip  across  the 

form  at  time  of  laying. 


PLATE  VII. 


VIEW     SHOWING     THE     METHOD    OF    USING    PARTING    STRIPS 
HOOKED    OVER    SIDE    FORMS. 


PLATE  VIII. 


View  Showing  Expansion  Cracks  formed  at  Marks. 


Exaggerated  Section  Showing  Contorted  Surface  when  Cracks  are 
Formed  at  Markings. 


GOOD  CONCRETE 


3! 


Various  Types  of  Parting  Strips 


Side  form  notched  I ' 


Strip  in  place 


\ 


Slot  in  side 
form      ' 


Steel 


Side  form 


Steel 


Smith  Patent  Rail  Clamp 

X*  Steely /• 

~T~ 


Zeiser  Patent 


Wedge    X 


«2 GOOD  CONCRETE 

Method       Parting  strips  if  made  of  steel  and  of  types  a,  b,  c  or  d,  Fig.  4. 
of  using  act  as  ties,  bracing  the  side  forms.     The  parting  strips  must  be  so 
parting  spaced  that  they  will  come  at  the  exact  point  where  a  cross  mark 
strips  is  to  be  made.     They  are  placed  at  every  alternate  block  division, 
or  they  can  be  placed  at  every  third  block  division.     Thus  if  the  side- 
Fading  walk  is  to  be  divided  into  2'  blocks  by  the  marking  then  the  parting 
strips  must  strips  will  be  placed  A'  apart  in  the  first  instance,  and  6'  apart  in 
coincide  the  second.     These  parting  strips  are  left  in  until  the  concrete  base 
with  block  and  top  have  been  placed  and  are  removed  just  before  the  top  is  to 
marking  be  floated  with  a  steel  finishing  float. 

Joints  must       In  finishing  over  the  joint  left  by  the  removal  of  the  parting  strips, 

be  kept  a  pointing  trowel  should  be  run  down  into  the  joint  to  cut  any  of  the 

open  top  mortar  that  might  be  forced  into  it  by  ths  float;  it  is  then  "edged" 

by  means  of  the  "jointing"  or  marking  tool. 

Other       In  some  localities  an  expansion  joint   1 "  wide  is  placed  at  every 

methods  of  50  feet  of  the  walk.     This  method  is  preferable  to  "no  joints"  at  all, 

providing  but  dees  not  provide  for  the  shrinkage.     A  joint  1 "  wide  every  50' 

for  expansion  is  rather  unsightly.     Appearance  alone  would  favor  distributing  the 

joints  as  is  done  by  the  use  of  parting  strips.     Beaver  Board,  if  used, 

may  be  placed  every  1 0'  and  left  in  the  work.     It  is  elastic  enough 

to  give  the  proper  relief. 

The  1"  joint  is  usually  filled  with  asphalt  or  pitch.  The  joint 
left  by  the  parting  strips  need  not  be  filled  with  any  mastic  material. 
If  the  contractor,  however,  deems  it  necessary  to  fill  them  they  should 
be  filled  only  about  two-thirds  of  their  depth.  This  will  prevent 
the  asphalt  or  pitch  oozing  out. 

PREPARATION  OF  THE  CONCRETE  AND  MORTAR. 

The  base  is  composed  of  concrete,  on  top  of  which  is  placed  the 
wearing  coat  of  mortar.  The  base  varies  in  thickness  from  3"  to  6" 
and  the  wearing  coat  from  J4"  to  %" ,  depending  upon  the  kind 
of  work. 

Concrete       The  first  consideration  should  be  density   (see  page  58).      This 
for  the  base  calls  for  a  balanced  mixture  of  coarse   and  fine  aggregate.      The 


GOOD  CONCRETE 


83 


84 GOOD  CONCRETE 

coarse  aggregate  is  either  gravel  or  crushed  rock  which  refuses  a  "4" 
screen  and  all  of  which  passes  a  1  Yi "  screen.  Stones  larger  than 
1  Yi"  for  a  base  less  than  4"  thick  will  be  found  troublesome.  It 
will  not  tamp  or  spade  readily.  The  fine  aggregate  must  all  pass  a 
YA"  screen. 

Coarse       The  coarse  aggregate  must  be  composed  of  crushed,  durable  rock 
aggregate  or  a  natural  screened  gravel.  Either  material  must  be  free  from  sur- 
face coatings  of  clay,  loam  or  other  foreign  substances   (see  pages 
17-21). 

Fine       It  has  already  been  pointed  out  that  the  strength  of  a  concrete  de- 
aggregate  pends  upon  the  strength  of  the  binding  mortar  (See  page  1  7). 

The  strength  of  the  mortar  will  of  course  depend  upon  the  sizing 
of  the  sand  particles  and  the  amount  of  cement,  (See  pages  21-26). 

The  best  sands  are  those  in  which  the  particles  grade  down  from 
coarse  to  fine,  giving  a  regular  Mechanical  Analysis  curve. 

Plate  1  shows  various  types  of  sands.     For  the  purpose  of  side- 
walk construction  a  sand  should  have  the  following  sizing: 

100%  should  pass  a  J4"  sieve. 

Not  less  than  30%  or  more  than  70%  shall  pass  a  No.  20  sieve. 

Not  more  than  30%  shall  pass  a  No.  50  sieve. 

Not  more  than  5%  shall  pass  a  No.  100  sieve. 

Generally  the  larger  the  percentage  of  very  fine  sand  (finer  than  50 
mesh)  the  more  cement  will  be  necessary  to  give  the  requisite  strength. 
The  sand  must  be  free  from  organic  matter  such  as  roots,  grass,  or 
soil  humus.  It  must  not  contain  more  than  5%  of  clay  and  the  clay 
must  not  be  present  as  a  coating  on  the  sand  grain. 

Rock  Screenings  from  crushed  trap  rock  or  limestone  that  will  all  pass 
screenings  a  Y*"  screen  can  be  used  to  good  advantage  in  place  of  sand  or 
as  an  addition  to  it  (see  page  30).  The  requirements  for  sizing 
of  particles  for  screenings  are  confined  only  to  all  of  the  material  pass- 
ing a  YA"  screen  and  freedom  from  dirt.  The  large  percentage  of 
fine  material,  as  long  as  it  is  all  rock  dust,  is  no  objection,  as  has 
already  been  explained  on  page  3 1 . 


GOOD  CONCRETE  85 

In  proportioning  the  cement,  sand  and  coarse  aggregate,  the  quan-  Proportioning 
tities  must  be  measured  by  volume,  and  not  guessed  at.     The  pro-  the  concrete 
portion  of  cement  to  total  aggregate  should  not  be  greater  than   I 
part  cement  to  8  parts  aggregate. 

It  has  already  been  dwelt  upon  that  the  arbitrary  proportioning  Proportion 
of  sand  and  crushed  stone  is  a  very  unscientific  procedure,  since  all  of  fine  to 
crushed  rock,  gravel  and  sand  does  not  contain  the  same  percentage  coarse 
of  voids.      The  amount  of  cement  has  been  already  specified  and  aggregate 
represents  the  quantity  that  has  by  experience  been  found  to  be  best 
suited  for  this  particular  purpose.     It  remains  to  find  the  best  propor- 
tion of   sand  to  coarse  aggregate.      This  can  be   accomplished  by 
either  of  three  methods: 

( 1  )      By  determining  the  voids  in  the  coarse  aggregate. 

(2)  By  the  Synthetic  volumetric  method. 

(3)  By  the  Concrete  law. 

These  methods  are  described  in  detail  under  the  heading  "Propor- 
tioning Concrete"  (pages  37-42).  By  whatever  method  propor- 
tioned, the  object  sought  is  the  proportion  which  will  give  the  densest 
mixture. 

Perhaps  the  most  convenient  method  of  determining  the  proportion 
of  coarse  to  fine  aggregate  for  sidewalk  work  will  be  the  method 
depending  on  the  determination  of  the  voids  in  the  rock,  and  adding 
a  volume  of  sand  equal  to  the  voids  in  the  rock  plus  10%  (see  page 
38). 

In  many  communities  the  sidewalk  contractor  is  accustomed  to  use  Natural 
a  natural  mixture  of  gravel  and  sand  just  as  it  comes  from  the  stream  gravel  and 
bed  or  gravel  pit,  mixing  it  with  a  given  quantity  of  cement  Toithoui  crusher 
regard  to  the  proportion  of  coarse  to  fine  aggregate  (see  page  19).        run 

The  sand  and  gravel  are  seldom  if  ever  found  mixed  in  anywhere  Natural 
near  the  proper  proportions.  By  using  such  a  material  without  first  gravel 
determining  the  proportion  of  fine  to  coarse  and  correcting  it  by  the  must  be 
addition  of  that  aggregate  which  it  lacks  the  contractor  is  taking  a  screened 
chance  on  the  ultimate  outcome  of  the  work. 


86 GOOD  CONCRETE 

How  to       T^  test  to  determine  whether  or  not  the  coarse  and  fine  aggregate 

determine.  m  a  natural  gravel  is  balanced  is  so  extremely  simple  that  no  excuse 

the  balance  exists  for  not  making  it.     The  determination  of  the  voids  will  immedi- 

°f  a  ately  show  whether  the  material  is  balanced  or  not.     A  sieve  test 

natural  ^^  t^e  jvjo   4  sjeve  ^JJ  gjve  the  amount  of  each  material  which  the 

mixture  mixture  lacks 

A  good       There  must  be  at  least  ]/2  <*s  much  of  the  natural  material  pass  a 

rule  to  y^n  screen  as  n,,7/  remain  on  it.     If  less  than  Yi  of  the  material  (by 

follow  volume)  passes  the  No.  4  sieve  then  MORE  SAND  will  have  to  be 

added  to  bring  it  up  to  Yz-     If  more  than  Yi  passes  the  Yt,"  sieve 

then  more  rock  will  have  to  be  added. 

Unscreened       jf  crushed  from  clean  durable  rock,  can  be  used  just  as  is  natural 
crushed  rock  or  gravel  jf  tne  same  precautions  are  observed  to  see  that  the  coarse  and 
crusher  run  fine  portions  are  properly  balanced. 

The  consistency  of  the  concrete  for  the  base  is  not  to  be  quite  as 

'tiecolicrefe  plastic  as  that  U8ed  f°r  Other  claSSCS  °f  WOfk-     II  sh°uld  be  iust  SO 
for  the  base  wet  l^at  'l  cannot  be  tamped  much  before  it  will  "quake." 

Mixing       This  is  either  done  by  hand  or  by  a  machine  mixer.      Machine 

the  concrete  mixing  is  preferable.      For  either  method  the  reader  is  referred  to 

pages  48-50,  bearing  in  mind  that  the  proper  and  thorough  mixing 

is  a  most  important  operation,  and  one  upon  which  the  success  of  the 

work  will  largely  depend. 

PROPORTIONING  THE  MORTAR  FOR  THE  WEARING  COAT. 
Proportions  The  proportion  of  cement  to  sand  will  depend  largely  upon  the 
fineness  of  the  sand.  A  fine  sand  will  need  more  cement  than  will  a 
well-graded  coarse  sand.  On  page  56  attention  has  already  been 
called  to  the  objection  of  using  too  rich  a  mortar.  Such  a  mortar  will 
shrink  more  than  a  leaner  one,  and  will  develop  "craze  cracks." 
With  a  well-graded,  coarse  sand,  a  proportion  of  1  part  cement  to 
2 1/2  parts  sand  is  a  serviceable  mixture  and  one  that  will  not  develop 
an  undue  amount  of  crazing  if  it  is  not  over-troweled.  With  a  finer 
and  poorer  graded  sand  a  proportion  of  1  part  cement  to  1 Yz  parts 
sand  will  have  to  be  used. 


GOOD  CONCRETE  87 

The  sand  must  first  of  all  be  screened  through  a  1/4"  screen  to  Sand 
remove  any  oversized  material.  The  sand  must  be  free  from  nodules 
of  clay  or  soft  material,  and  the  percentage  of  grains  finer  than  50 
mesh  should  be  as  small  as  possible.  Nodules  of  clay  will  "dissolve," 
leaving  pit  marks  in  the  finished  surface.  Soft,  friable  particles  are 
likely  to  puff  and  blister  the  finished  surface.  Sand,  where  sizing 
conforms  to  that  given  under  sand  for  the  base,  with  the  exceptions 
above  noted,  will  answer. 

Upon  the  method  of  mixing  will  depend  the  ease  with  which  the  Mixing 
top  will  work  under  the  trowel. 

The  sand  and  cement  are  first  thoroughly  mixed  dry  to  a  uniform 
color,  in  a  watertight  mortar  box.  The  mixed  materials  are  then 
spread  out  over  the  bottom  of  the  box  and  "craters"  formed,  into 
which  about  half  of  the  necessary  water  is  added  and  allowed  to 
"soak  up"  for  from  1  5  to  20  minutes.  The  mass  is  then  worked 
thoroughly,  adding  the  additional  water  necessary  to  produce  the 
desired  consistency,  in  a  fine  spray.  The  water  should  be  less  than 
what  looks  to  be  enough  for  a  given  consistency.  Upon  further  work- 
ing the  mass  with  the  hoe,  it  will  be  found  to  become  "wetter"  and 
"smoother."  This  is  due  to  the  cement  becoming  plastic.  If  all 
the  water  is  added  at  once  the  mortar  will  work  "short,"  in  as  much 
as  the  cement  has  not  had  time  to  soak  up  the  necessary  water  to  soften 
it.  The  cement  particles  must  be  converted  into  the  gelatinous  condi- 
tion by  contact  with  the  water  before  it  can  be  expected  to  work 
smooth.  When  a  top  finish  works  "sandy"  it  is  usually  due  to  the 
cement  particles  not  having  become  gelatinous.  The  same  effect  is 
produced  by  a  large  percentage  of  "quick  sand"  in  the  mortar  which 
floats  and  works  to  the  top  under  the  action  of  the  trowel. 

The  average  sidewalk  maker  makes  his  top  extremely  n?e/,  so  wet  Consistency 
that  the  cement  and  sand  will  segregate  if  left  standing  a  few  minutes.   Of  the 
A  mortar  as  wet  as  this  is  of  course  very  easy  to  float  on  to  the  base,   mortar 
It  is  contrary  to  good  and  proper  practice  to  make  the  mortar  as 
"sloppy"  as  this.     It  greatly  diminishes  the  resistance  to  wear  of  the 
hardened  top  and  has  other  disadvantages  that  will  be  considered  later. 


88 


GOOD  CONCRETE 


SIDEWALKS. 


TABLE  XV. 
-QUANTITIES  FOR  BASE 


Proportion 
by  Vol. 

Thickness 
of  Base 

No.  Sq.  ft.  of 
Base  from 
1  cu.  yd. 
Concrete 

No.  sq.  ft.  of 
Base 
per  Sack 

:2:4 

6    " 

54.0 

8.5 

:2:4      ' 

5    " 

65.6 

10.4 

:2:4 

4   " 

81.0 

12.8 

:2:4 

3    " 

108.0 

17.0 

:2:4 

2K» 

123.0 

19.3 

:2^:5 

6   « 

54.0 

10.9 

:21A:5 

5    " 

65.6 

12.5 

:2#:5 

4    » 

81.0 

15.4 

:2^:5 

3    • 

108.0 

20.5 

:2#:5 

2*" 

123.0 

23.5 

:3:6 

6   " 

54.0 

12.7 

:3:6 

5    • 

65.6 

15.5 

:3:6 

4    " 

81.0 

19.0 

:3:6 

3    » 

108.0 

25.4 

:3:6 

2^" 

123.0 

27.6 

SIDEWALKS-QUANTITIES  FOR  TOP 
Square  Feet  per  Sack 


Proportion 


Thickness  of  Top 


Grill. 

Sd. 

X* 

h* 

1.01 

w 

2.0" 

1 

1 

33.12 

22.08 

16.56 

11.04 

7.28 

1 

I* 

41.76 

27.84 

20.88 

13.93 

10.44 

1 

2 

50.64 

33.76 

25.32 

16.88 

12.66 

1 

2X 

58.48 

38.98 

29.24 

19.50 

14.62 

1 

3 

67.92 

45.28 

33.96 

22.64 

16.98 

GOOD  CONCRETE 89 

The  proper  consistency  of  the  mortar  should  be  such  that  it  can 
just  be  "rodded"  without  "pulling"  and  just  so  wet  that  it  will  not 
"stand  up,"  but  will  flatten  out  in  a  few  seconds,  so  wet  that  it  cannot 
be  shoveled,  but  will  have  to  be  dipped  out  in  a  bucket.  It  must  not 
be  wet  enough  to  allow  the  cement  and  sand  to  separate. 

Cement  is  considerably  heavier  than  sand  and  has  a  natural  tend- 
ency to  separate  from  it  in  the  presence  of  too  much  water.  If  each 
cement  particle  is  gelatinous  it  will  stick  to  the  sand  with  great  tena- 
city, thus  forming  a  viscous  mass.  It  is  the  production  of  this  viscous 
mass  that  is  the  object  sought  in  a  mortar  for  finishing. 

PLACING  THE  CONCRETE  AND  MORTAR. 
ORDINARY  TYPE  OF  RESIDENCE  SECTION  SIDEWALK. 

On  the  sub-base  or  foundation  which  has  been  excavated  to  grade  Forms 
and  tamped  the  side  forms  are  placed.  The  top  of  the  forms  should 
conform  to  the  finished  grade  as  given  by  the  Engineer.  The  form  on 
the  side  nearest  the  curb  is  placed  a  little  lower,  so  as  to  give  the  walk 
drainage  toward  the  curb.  The  forms  are  usually  made  of  surfaced 
2"  stuff  with  the  depth  corresponding  to  the  total  depth  of  the  con- 
crete base  and  top.  The  surface  of  the  lumber  must  be  cleaned  of  any 
adhering  mortar  and  wetted  before  the  concrete  is  deposited.  On  the 
top  of  the  side  forms  marks  are  made  where  each  block  division  will 
come.  The  parting  strips  are  then  placed  and  the  forms  lined  up  true 
to  the  established  lines  and  staked. 

The  sub-base  is  then  wetted  and  the  concrete  filled  into  the  forms  Depositing 
and  tamped,  using  the  "templet"  shown  in  Fig.    1 .     The  notch  is  the  concrete 
equal  to  the  thickness  of  the  top.     The  tamping,  should  be  most  thor- 
ough, so  that  the  concrete  surface  will  present  a  uniform  appearance. 
The  proper  consistency  of  the  concrete  will  produce  a  mass  that  will 
quake  very  readily  under  moderate  tamping,  and  one  that  will  spade 
readily.     Next  to  the  form  a  shovel  or  trowel  should  be  run  down 
to  "turn"  any  "arched"  stones.     The  concrete  should  be  deposited  on 
both  sides  of  the  parting  strips  and  so  tamped  as  to  not  "bulge"  the 
strips. 


90 


GOOD  CONCRETE 


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GOOD  CONCRETE 91 

The  batches  of  concrete  should  not  be  mixed  larger  than  can  con-   Size  of 
veniently  be  deposited  within  30  minutes.     After  the  base  has  been   batch  of 
placed,  tamped  and  brought  to  the  proper  level,  the  top  is  immedi-  concrete 
ately  placed  by  first  spreading  it  on  the  base  in  a  thin  layer  and 
trowelling  it  thoroughly  to  make  a  bond  on  the  concrete  and  then 
pouring  and  spreading  to  the  top  of  forms  and  levelling  off  with  the 
floating  rod   (Fig.    1).     The  floating  rod  should  be  given  a  "back 
and  forth"  motion  in  levelling  off  the  top,  and  not  moved  straight 
ahead. 

The  top  must  be  placed  not  more  than  30  minutes  after  the  con-   Placing 
crete  base  is  in  place.     If  the  base  dries  out  before  the  top  is  placed    the  top 
and  worked  into  it,  a  poor  bond  is  produced,  which  will  result  in  a 
"loose  top."     If  base  does%dry  out  before  top  is  placed  it  may  be 
sprayed  gently  with  water. 

After  levelling  the  top  by  means  of  the  "floating  rod"  it  is  left   Finishing 
untouched  until  the  water  begins  to  leave  the  surface,  i.  e.,  at  the    the  top 
point  at  which  the  surface  of  the  mortar  loses  its  gloss,  and  just  begins 
to  stiffen  up  slightly.      It  is  then  gone  over  with  the  wooden  float  and 
rubbed  up.      The  parting  strips  are  now  removed  and  the  surface 
blocked  off  into  the  sized  blocks  desired  by  the  length  and  crosswise 
markings,  using  a  "jointer,"  and  the  edges  next  to  the   forms  are 
rounded  off  with  the  "edging  tool."     At  the  joint  left  by  each  part- 
ing strip  a  pointing  trowel  is  run  down  to  insure  the  complete  separa- 
tion of  the  blocks  between  the  parting  strips. 

If  a  rough  finish  is  desired  the  surface  is  roughened  inside  the  block    Rough 
markings,  leaving  the  border  made  by  the  "jointer."     The  "rough-    finish 
in?"  is  accomplished  by  brooming  or  with  a  wooden  float  to  which 
a  rotary   motion  is  given.      This  procedure  produces  a  serviceable 
roughened  surface  that  is  rather  pleasing  to  the  eye. 

If  an  ordinary  smooth  finish  is  desired  the  surface  is  lightly  trow-    Smooth 
eled  with  the  steel  float  after  marking  and  edging.     If  a  high  polish    finish 
is  desired  the  top  is  allowed  to  stiffen  up  well  before  it  is  "rubbed  up" 
with   the  wooden   float,    marked   and   edged.      The  polish   is   them 


92  GOOD  CONCRETE 

obtained  by  troweling  with  a  steel  float.  To  get  a  polish  the  initial 
set  of  the  mortar  is  broken  down.  A  polished  surface  will  always 
craze  after  a  longer  or  shorter  time.  It  is  the  least  serviceable  finish 
that  can  be  given  a  sidewalk. 

Dusting  The  practice  of  "dusting"  neat  cement  upon  the  surface  to  make 
it  finish  easily  is  one  often  indulged  in  by  the  finisher.  Such  a  pro- 
cedure, although  producing  a  smooth  finish,  will  cause  the  surface 
to  craze  badly. 

Effect  of        All  Portland  Cement  contains  a  small  amount  of  gypsum,  which 

working  *8  added  to  control  the  setting  time.     The  gypsum  is  relatively  soft 

the  top   and  light.      In  grinding  the  clinker  the  gypsum  naturally  is   more 

too  wet   easily  reduced  to  flour,  and  will  be  much  finer  than  the  finished 

cement.     Now,  then,  if  the  top  mortar  is  worked  too  wet  this  gypsum 

flour  will  "slime"  to  the  surface  under  the  action  of  the  floating 

rod.      In  levelling  off  with  the  floating  rod  a  very  thin  and  "slimy" 

liquid  will  be  shoved  ahead  of  the  rod.     This  liquid  contains  most 

of  the  gypsum  and  the  surface  rodded  will  be  deficient  in  relarder 

and  at  the  points  where  the  rod  is  lifted  and  the  thin  grout  distributed 

by  troweling  the  surface  will  have  an  excess  of  gypsum,  so  that  the 

surface  first  mentioned  will  set  up  very  rapidly,  whereas  the  other 

surface  will  set  up  exceedingly  slowly.     This  peculiarity  is  usually 

attributed    to    the    cement.      The    occurrence,    however,    is    positive 

evidence  that  the  worker  has  worked  the  top  too  sloppy. 

Again,  the  thin  grout  resulting  from  too  much  water  forms  "lai- 
tance"  (see  page  15),  which  covers  the  surface  as  a  thin  film. 
This  film  does  not  "set  up,"  but  dries  out  to  a  soapstone-like  sub- 
stance which  wears  off  under  traffic  and  leaves  the  surface  "sandy" 
and  mottled. 

Colored        If  the  surface  is  to  be  colored  the  coloring  matter  is  added  to  the 
mortar  mortar  and  should  never  be  sprinkled  or  dusted  on  the  surface  just 
before  finishing.      The  quantities   and   kinds  of  color  necessary   to 
produce  a  given  color  will  be  found  on  page  90,  table  XVI. 


GOOD  CONCRETE 22 

The  method  of  laying  a  sidewalk  extending  from  the  building  line  Laying  full 
to  the  curb  differs  only  in  some  details  from  that  used  for  the  ordi-   width 
nary  sidewalk.     The  chief  difference  being  in  the  laying  of  guide  Sidewalks  in 
strips  at  right  angles  to  the  direction  of  the  walk  to  facilitate  getting  business 
an  even  surface.      These  guide  strips  are  placed  from  4'  to  6'  apart  sections 
and  are  given  the  grade  that  the  finished  surface  is  to  have.     They 
are  usually  made  of   1"  or  2"  stuff,  having  a  depth  equal  to  the 
thickness  of  the  base  and  top.     These  strips  also  act  as  parting  strips. 
They  are  left  in  until  after  the  top  is  floated,  then  removed  and  filled 
with  mortar.     The  strips  should  be  so  placed  as  to  come  out  at  block 
markings.     As  soon  as  the  mortar  has  stiffened  in  the  grooves  left 
by  the  guide  strips  a  cut  through  to  the  sub-base  is  made  by  means 
of  a  trowel  guided  by  a  straight  edge.     A  joint  at  least  y%"  wide 
should  be  left  between  the  curb  and  the  sidewalk. 

The  sidewalk  contractor  will  often  be  called  upon  to  lay  floors  Laying 
on  a  base  of  concrete  that  has  been  in  place  some  time;     There  are  floors  on  a 
certain  precautions  to  be  observed  in  such  cases  to  insure  the  perma-  hardened 
nence  of  the  work.     Such  floors  will  usually  consist  of  an  application  concrete 
of  mortar  to  the  hardened  concrete  base.     The  "finish"  should  never  base 
be  less  than  1  J/fc"  in  thickness.     The  concrete  base  is,  first  of  all, 
thoroughly  "roughened"  by  picking  the  surface  with  a  gad  or  other 
proper  tool.     It  is  then  brushed  clean  and  thoroughly  rinsed  with 
running   water.      The   old   concrete   must   be   thoroughly   saturated 
with  water  before  the  top  is  placed. 

Guide  strips  are  then  placed  as  above,  and  a  thin  grout  of  neat 
cement  is  scrubbed  into  the  surface  of  the  old  concrete,  upon  which 
the  top  is  immediately  placed  and  vigorously  troweled  into  the  base. 
The  top  is  then  rodded  off  just  as  in  sidewalk  work,  marked  and 
finished  after  the  guide  strips  are  removed  and  the  joints  left  by 
them  filled  with  mortar. 

The  marking  should  be  so  arranged  and  laid  out  that  marks  will   Marking 
come  over  the  center  of  all  beams  and  girders.     At  these  points  the 
marks  should  be  cut  through  to  the  base  (expansion  joint),  and  the 


94 GOOD  CONCRETE 

marks  cut  through  to  the  base  in  such  a  manner  as  to  divide  the 
whole  floor  into  separate  blocks  not  greater  than  6'  on  a  side. 

GENERAL  REMARKS. 

In  localities  that  are  very  dusty  and  windy  in  summer  the  side- 
walk worker  cannot  be  too  careful  to  prevent  dust  settling  on  the 
concrete  base  before  the  top  is  placed.  A  film  of  dust  will  prevent 
a  proper  bond  between  the  top  and  the  base.  He  should  therefore 
wet  down  the  pile  of  excavated  material  lying  alongside  of  the  work. 
The  workmen  should  also  be  prevented  from  carrying  dust  and  dirt 
on  to  the  base  in  carrying  the  top  mortar  for  pouring. 

S«e  oj        The  blocks   into  which  the   surface  is   divided  by   the   marking 
blocks  should  not  be  larger  than  3'  on  a  side.      The  smaller  the  blocks 
the  less  danger  from  cracking. 

Finishing  Jn  finishing  the  surface  should  not  be  troweled  too  much,  as  in 
so  doing  all  the  neat  cement  is  brought  to  the  top  by  the  "suction" 
of  the  float.  A  rough  surface  is  more  serviceable  than  a  highly 
polished  one.  A  rough  surface,  if  properly  fringed  by  the  mark 
made  with  the  "jointer"  is  as  artistic  as  a  highly  polished  one. 

Roughing  can  be  accomplished  by  means  of  the  "float  suction," 
grooving  with  a  toothed  roller,  or  brushed  with  a  stiff  broom.  In 
extremely  fine  work,  such  as  porch  floors,  a  serviceable  finish  can 
be  made  by  rubbing  the  surface  with  a  carborundum  brick  after 
the  top  has  hardened  for  six  or  seven  days. 

Air       In  troweling  a  surface  the  finisher  will  often  notice  the  formation 
bubbles  Of  "blisters."     These  are  caused  by  entrained  air.     They  should  be 
punctured  and  pressed  out  before  set  takes  place.      If  not  removed 
they  will  eventually  cause  a  loose  top  by  the  air  expanding. 

Protecting       The   surface   must   be   protected    against   premature   drying   out. 

the  green  If  the  work  is  done  in  a  strong  draft  draw  cracks  will  form  before 

surface  the  top  sets  up.     These  draw  cracks  open  up  parallel  to  one  another 

and  usually  at  right  angles  to  the  direction  of  the  draft.      A  low 


GOOD  CONCRETE 


95 


screen  placed  to  the  windward  will  effectually  prevent  the   forma- 
tion of  these  cracks. 

As  soon  as  the  top  has  taken  on  hard  set,  it  should  be  covered  Covering 
with  sand  or  dirt,  which  is  then  wetted  at  least  once  a  day  for  several  the  work 
days  to  thoroughly  "cure"  the  top. 

If  water  is  applied  direct  to  the  surface  it  should  only  be  done 
in  the  morning.  If  cold  water  is  squirted  on  to  the  top  while  it  is 
hot  or  warm,  cracks  can  result  from  the  sudden  cooling. 

Cement  is  a  poor  conductor  of  heat;  it  warms  up  slowly  and  cools  Precaution 

slowly.      A  cement  mass  exposed  to  the  sun  during  the  day  will  in  the 

retain  a  great  deal  of  heat  for  many  hours  after  sundown.     It  prac-  use  of 

tically  takes  it  all  night  lo  cool  off.     Water  therefore  should  only  water  on 

be  applied  to  a  "green"  sidewalk  early  in  the  morning.     After  the  green 

work  has  aged   for  some  weeks  it  can  safely  withstand  the  shock  cement 
of  cold  water  applied  during  the  heat  of  the  day. 

If  ordinary  earth  is  used  to  cover  the  green  work  it  should  be 
free  from  soil  humus.  The  acid  in  the  humus  will  permanently 
discolor  the  surface.  Adobe  also  has  a  tendency  to  discolor  the 
surface  where  so  used. 


Causes  of  Defects  in 
Sidewalks 


Proper  Method  of  Stopping  a  Days  Work 


Header  must  be  placed 
even  with  a  block  mark 


Improper  method 
of  stopping 


Fig.  6. 


PLATE   IX. 


CRACK      FOLLOWING      THE      LENGTHWISE      MARKING.         CRACK 
CAUSED    BY    ADOBE    FOUNDATION    SWELLING. 

Remedy: — Prepare  Foundation  as  shown  in  Fig.  2. 


PLATE  X. 


LOOSE  TOP.     CAUSED  BY  POOR  BOND  BETWEEN  BASE  AND  TOP 


PLATE  XL 


Effect  of  Expansion  on  End   of  Sidewalk  Caused  by  the  Whole 
Length  Creeping,  Due  to  Absence  of  Expansion  Joints. 

73 


Here  the  length  of  A-B  was  sufficiently  strong  to  not  crack  on 
being  thrust  up  as  shown.  The  curb  C  being  buried  prevented  any 
horizontal  movement  in  the  direction  of  the  arrow,  making  the  walk 
lift  itself. 

A  73 


m 

P  ':Q:-'O-  ,  '•  0.'.  •(>.'-  0  -  O  '•  £>••£>  •  :.D  "•  •'  'p':  '.  '!£'.'•'  -&\  0  o  0'°£?  't>"-'0.:'o  *? 

§! 

Remedy: — Cut  through  the  base  by  parting  strips  at  points  A-B 
and   at  each   alternate  block  division. 


PLATE  XII. 


Example  of  the  Effect  of  Expansion.      Corner  Block  Shoved  Bodily 
Out  of  Place. 


Cause: — The  expansion  from 
two  directions  A  and  B  have 
combined  to  shove  the  corner 
in  the  direction  C. 


Remedy: — Provide  ]/$"  expansion  joints  every  alternate  block 
division  along  A  and  B.  Make  the  corner  entirely  separate,  pro- 
viding '/4  "  joints  cut  through  the  base  at  D-E. 


PLATE  XIII. 


The  Effect  of  Expansion  on  Corner  Blocks  of  Combined  Sidewalk 
and  Curb. 


vr». 


Cause: — Lack  of  provision   for  expansion. 

Remedy: — Make   corner  entirely  separate   from  the  rest  of  the 
walk.      Keep  curb  and  walk  separate. 


H  ^ 
£     .-S 


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£  cl 


l!P 

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s  fe£'£ 


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Curbs  and  Gutters 


CHAPTER  VI. 


CURBS  AND  GUTTERS. 

The  same  general  principles  governing  the  use  of  cement  for  side- 
walks apply  to  the  construction  of  curbs  and  gutters. 

From  the  nature  of  the  construction,  more  provision  for  expansion  Expansion 
and  shrinkage  is  necessary  in  a  curb  than  in  a  sidewalk.     A  curb  and 
has  about  J/2  of  its  mass  buried.     As  the  street  side  of  the  curb  acts  shrinkage 
as  a  gutter,  the  gutter  will  usually  be  more  or  less  moist.      In  this 
moist  environment  concrete  will  expand  instead  of  shrink   (see  page 
55).      That  is,  one  half  of  the  curb  will  be  shrinking  while  the  re- 
mainder will  be  expanding.     This  condition  produces  stresses  in  the 
concrete,   which   inevitably   causes   more   or   less   vertical   cracks   at 
intervals  of  from  8  to    12   feet.      For  work  done  in  cool  weather 
the  combined  thermal  expansion,  shrinkage  and  normal  expansion, 
can  with  the  advent  of  warm  weather  produce  most  destructive  ef- 
fects, as  shown  in  Plates  XV-XVI. 

To  provide  for  these  factors  the  curb  or  curb  and  gutter  must  be  Provision  for 
separated  during  construction  into  separate  blocks  by  means  of  part-  expansion 
ing  strips.  and  shrinkage 

Figs.  7  and  8  show  the  details  of  such  construction  for  all  of 
the  types  of  construction.  The  following  specifications  will  be  found 
to  give  excellent  work  if  closely  followed: 


102  GOOD  CONCRETE 

SPECIFICATIONS   FOR   CONCRETE   AND   GUTTER. 

MATERIALS. 

Cement  T^e  cement  shall  be  Riverside  Portland  and  meet  the  require- 
ments of  the  Standard  Specifications  for  Portland  Cement  of  the 
American  Society  for  Testing  Materials. 

Fine        The  fine  aggregate  shall  consist  of  sand,  crushed  stone  or  gravel, 
aggregate  screenings,   conforming  in  composition   and   grading  of  particles  to 
the  requirements  set  for  sidewalk  work  on  page  84. 

Coarse        Coarse  aggregate  shall  consist  of  inert  materials  graded  in  size, 
aggregate  such  as  crushed  stone  or  gravel,  which  are  retained  on  a  screen  hav- 
ing one-quarter    (|/4)    inch  diameter   holes,   shall   be   clean,   hard, 
durable  and  free  from  all  deleterious  matter.     Aggregates  consisting 
of  soft,  flat  or  elongated  particles  shall  be  excluded. 

The  maximum  size  of  the  coarse  aggregate  shall  be  such  that  it  will 
not  separate  from  the  mortar  in  laying  and  will  not  prevent  the  con- 
crete from  filling  all  parts  of  the  forms.  The  size  of  the  coarse 
aggregate  shall  be  such  as  to  pass  a  one  and  one-quarter  ( 1  '/4 )  inch 
ring. 

Natural       Natural  deposits  of  sand  and  gravel,  usually  being  out  of  balance, 
mixed  s^a^  be  screened  and  remixed  to  agree  with  the  proportions  specified 
aggregates  «n<kr  Base. 

Water        Water  shall  be  clean,  free  from  oil,  acid,  strong  alkalies  or  vege- 
table matter. 

Expansion  The  expansion  joint  filler  shall  be  Beaver  Board  or  a  suitable  elastic 
joint  waterproof  compound  that  will  not  become  soft  and  run  out  in  hot 
filler  weather  or  hard  and  brittle  and  chip  out  in  cold  weather. 

SUB-GRADE. 

Depth  fee/on?        When  a  sub-base  is  required  the  sub-grade  shall  be  not  less  than 
grade  of  gutter  t™6^6  02)  inches  below  the  finished  surface  of  the  gutter. 

Depth  of        AH  s°ft  or  8P°n8y  places  shall  be  removed  and  all  depressions 
layers   ^Hed  with  suitable  filling  material,  which  shall  be  thoroughly  com- 


GOOD  CONCRETE  103 


pacted  by  flooding  and  camping  in  layers  not  exceeding  six    (6) 
inches  in  thickness. 

When  a  fill  exceeding  ( 1 )   foot  in  thickness  is  required  to  bring  Deep  fills 
the  work  to  grade  it  shall  be  made  in  a  manner  satisfactory  to  the 
engineer. 

When  required,  a  suitable  drainage  system  shall  be  installed  and  Drainage 
connected  with  sewers  or  other  drains  indicated  by  the  engineer. 

SUB-BASE. 

A  sub-base  shall  be  provided  if  required  by  the  engineer,  com-    Width 
posed  of  cinders  or  other  suitable  material   hereinbefore  specified,   Thickness 
which  shall  be  rammed  thoroughly  to  a  surface  at  least  six   (6) 
inches  below  the  finished  surface  of  the  gutter. 

While  compacting  the  sub-base  the  material  shall  be  kept  thor-   Wet 
oughly  wet  and  shall  be  in  that  condition  when  the  concrete  is  de-  material 
posited. 

FORMS. 

Forms  shall  be  free  from  warp,  and  of  sufficient  strength  to  resist  Material 
springing  out  of  shape.     All  mortar  and  dirt  shall  be  removed  from 
forms  that  have  been  previously  used. 

The  forms  shall  be  well  staked  or  otherwise  held  to  the  established  Settings 
line  and  grade,  and  their  upper  surface  shall  conform  with  finished 
surfaces  of  the  curb  and  gutter,  respectively. 

All  forms  shall  be  thoroughly  wetted  before  any  material  is  de-   Wetting 
posited  against  them. 

DIMENSIONS. 

The  section  of  the  curb  shall  conform  to  those  shown  in  Figs.  7  Curb 
and  8. 

The  thickness  at  the  base  shall  not  be  less  than  twelve  (12)  inches 
and  the  thickness  at  the  top  not  less  than  six  (6)  inches,  with  a 
batter  on  the  street  side  of  one  (1 )  to  four  (4). 


104 


GOOD  CONCRETE 


Curb  and        The  sections  of  the  combination  curb  and  gutter  shall  conform 
gutter    with  those  shown  in  Fig.  8. 

The  depth  of  the  back  of  the  curb  shall  not  be  less  than  twelve 
(12)  inches  and  the  depth  of  the  face  not  less  than  six  (6)  inches. 
The  breadth  of  the  gutter  shall  not  be  less  than  sixteen    (16) 
inches  nor  more  than  twenty-four  (24)  inches. 

CONSTRUCTION. 

Size  of         The  curb  and  gutter  shall  be  divided  into  sections  not  less  than 

section    five  (5)  nor  more  than  eight  (8)  feet  long,  by  some  method  which 

will  insure  the  complete  separation  of  the  sections  by  a  joint  not 

less  than  one  one-eighth   C/g)   nor  more  than  one-quarter   (J/4)   of 

an  inch  wide. 

Section  at         The  construction   of  the   combination   curb   and   gutter   at  street 
street    corners  shall  conform  to  those  shown  in  Figs.  7  and  8.     The  radius  of 
corners    the  curve  shall  not  be  less  than  six  (6)   feet. 


CONCRETE. 

Proportions  The  concrete  for  the  curb  and  gutter  shall  be  so  proportioned 
that  the  cement  shall  overfill  the  voids  in  the  fine  aggregate  by  at 
least  five  (5)  per  cent,  and  the  mortar  shall  overfill  the  voids  in  the 
coarse  aggregate  by  at  least  ten  (10)  per  cent.  The  proportions 
shall  not  exceed  one  ( 1  )  part  cement  to  eight  (8)  parts  fine  and 
coarse  aggregates.  When  the  voids  are  not  determined,  the  concrete 
shall  be  composed  of  one  (1)  part  cement,  three  (3)  parts  fine 
aggregate  and  five  (5)  parts  coarse  aggregate. 

Measuring  The  method  of  measuring  the  materials  for  the  concrete,  including 
water,  shall  be  one  which  will  insure  separate,  uniform  proportion- 
ing at  all  times.  A  bag  of  cement  (94  pounds)  shall  be  considered 
to  have  a  volume  of  one  ( 1  )  cubic  foot. 


GOOD  CONCRETE 


The  ingredients  of  the  concrete  shall  be  thoroughly  mixed  dry,    Mixing 
sufficient  water   added   to  obtain   the   desired   consistency,    and   the 
mixing  continued  until  the  materials  are  uniformly  distributed  and 
the  mass  is  uniform  in  color  and  homogeneous. 

When  conditions  will  permit,  a  machine  mixer  of  a  type  which    Machine 
insures   the   uniform  proportioning  of   the   materials   throughout  the    mixing 
mass  shall  be  used. 

When  it  is  necessary  to  mix  by  hand,  the  mixing  shall  be  on  a  Hand 
water-tight  platform  and  the  materials  shall  be  turned  until  they  are  mixing 
homogeneous  in  appearance  and  color. 

The  materials  shall  be  mixed  wet  enough  to  produce  a  concrete    Consistency 
of  a  consistency  that  will  flush  readily  under  light  tamping  and  which 
can  be  handled  without  causing  a  separation  of  the  coarse  aggregate 
from  the  mortar. 


Retempering,  that  is,  mixing  with  additional  water,  mortar  or 
concrete  that  has  partially  hardened,  will  not  be  permitted. 

A  layer  of  concrete  shall  be  deposited  to  the  top  of  the  gutter  Placing 
form  and  tamped,  the  width  of  the  gutter,  to  a  surface  all  points  of 
which  shall  be  at  least  the  thickness  of  the  wearing  surface  below 
the  finished  surface  of  the  gutter.  The  concrete  placed  for  the  curb 
shall  be  tamped  and  the  remainder  of  the  concrete  placed  and 
tamped  to  permit  of  the  application  of  the  required  wearing  surface 
to  the  face  and  top  of  the  curb.  After  the  addition  of  water  the 
mixture  shall  be  handled  rapidly  to  the  place  of  final  deposit.  Under 
no  circumstances  shall  concrete  be  used  that  has  partially  hardened. 

Concrete  shall  not  be  mixed  or  deposited  when  the  temperature 
is  below  freezing  unless  special  precautions  are  taken  to  avoid  the 
use  of  materials  containing  frost  and  to  protect  the  work  against  frost 
until  thoroughly  hardened. 

Workmen  shall  not  be  permitted  to  walk  on  freshly  laid  concrete, 
and  where  sand  or  dust  collects  on  the  concrete  it  shall  be  carefully 
removed  before  the  wearing  surface  is  applied. 


106  GOOD  CONCRETE 


WEARING  SURFACE. 

Mixing  The  wearing  surface  shall  be  mixed  of  one  (  1  )  part  cement  and 
not  more  than  two  (2)  parts  fine  aggregate,  with  sufficient  water  to 
produce  a  consistency  which  will  not  require  tamping,  but  which  can 
be  easily  spread  into  position.  The  mortar  for  the  wearing  surface 
shall  be  mixed  in  a  mortar  box. 

Depositing  The  wearing  surface  shall  be  placed  immediately  after  mixing 
and  in  no  case  shall  more  than  fifty  (50)  minutes  elapse  between 
the  time  the  concrete  is  mixed  and  the  time  the  wearing  surface  is 
placed. 

Thickness       The  wearing  surface  on  the  gutter,  and  on  the  top  and  face  of 
the  curb,  shall  be  at  least  one-half  (Yi)  of  an  inch  thick. 


Marking      The  surface  and  edges  of  the  curb  and  gutter  and  joints  between 
sections  shall  be  finished  in  a  workmanlike  manner. 

Edges  The  edges  of  the  curb  on  the  street  side  and  the  intersection  of 
the  curb  and  gutter  shall  be  rounded  to  a  radius  of  about  one  and 
one-half  (IJ/z)  inches;  all  other  edges  to  have  a  radius  of  about 
one-half  (!/2>  inch. 

Troweling  When  required,  the  surface  shall  be  troweled  smooth.  The 
application  of  neat  cement  to  the  surface  in  order  to  hasten  the  harden- 
ing is  prohibited. 

Color  When  coloring,  matter  is  required  it  shall  be  mixed  dry  with  the 
sand  and  cement,  which  have  been  previously  mixed  dry,  until  the 
mixture  is  of  a  uniform  color.  The  quantity  and  quality  of  the 
coloring  shall  be  such  as  not  to  impair  the  strength  of  the  wearing 
surface. 

Protection  When  completed,  the  curb  and  gutter  shall  be  kept  moist  and  pro- 
tected from  traffic  for  at  least  one  (  1  )  week. 


Combined  Curb  ana  Gutter  Form 


Fig.  7. 


CO 
&b 


PLATE  XVIII. 
EXAMPLES  OF  THE  EFFECT  OF  EXPANSION  ON  CURBS. 


EFFECT    ALONG    CURB. 


X 

S>        — 

x   6 
£    tj 

-J       £ 

n        __ 

u 

UJ 

I 

H 

U. 

O 

3 

BU 

5 

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5 


PLATE  XXI. 
EXAMPLES  OF  GARDEN  WALLS. 


PLATE  XXII. 
EXAMPLES  OF  GARDEN  WALLS. 


PLATE  XXIII. 
EXAMPLES  OF  GARDEN  WALLS. 


CONCRETE   ROADS 


CITRUS    AVENUE,    LOS    ANGELES    COUNTY, 

CONCRETE    BASE   WITH   ONE-HALF   INCH 

BITUMINOUS  WEARING  SURFACE. 


CHAPTER  VII. 

CONCRETE  ROADS. 

INTRODUCTORY. 

A  good  road  should  provide  a  permanent,  even  surface  for  the 
travel  of  vehicles.  The  creation  of  an  even  surface  is  in  itself  an 
easy  matter,  but  the  maintenance  of  such  a  surface,  once  created 
within  the  bounds  of  economy,  is  not  an  easy  matter. 

The  water-bound  macadam  road  until  about  ten  years  ago  repre- 
sented the  best  type  of  highway  construction.  It  embodied  the  total 
accumulated  knowledge  of  the  road-building  art.  With  the  coming 
of  the  motor-vehicle,  defects  soon  developed  which  clearly  indicated 
the  inadequacy  of  this  type  of  construction  to  serve  the  demands  of 
the  new  traffic. 

Efforts  were  made  to  increase  the  resistance  of  the  macadam  road 
by  various  surface  applications.  In  every  case  such  measures  failed 
to  give  a  permanent  remedy.  The  road  builder  was  soon  brought 
to  the  realization  that  past  experience  offered  no  suggestions  for  the 
saving  of  the  waterbound  macadam  road  from  rapid  destruction  by 
motor  traffic. 

Highway  Engineers  in  all  parts  of  the  world,  pressed  by  the 
urgent  demand  for  a  better  road  for  the  changed  traffic  conditions, 
set  about  to  determine  the  factors  in  road  construction  that  make  for 


]2 GOOD  CONCRETE 

permanency.  The  past  decade  has  witnessed  more  experimental 
work  in  the  construction  of  highways  than  any  other  period  of  the 
world's  history.  The  first  problem  to  be  studied  was  the  cause  of 
the  rapid  destruction  of  macadam  by  rubber-tired  wheels. 

It  was  once  believed  that  the  "suction"  of  pneumatic  tires  removed 
the  binder  from  the  road.  A  rapidly  moving  automobile  will  raise 
a  cloud  of  dust  which,  it  is  true,  may  be  composed  of  the  binder, 
but  this  is  not  the  result  of  any  suction  on  the  part  of  the  pneumatic 
tire,  but  in  fact  the  effect  of  the  air  currents  set  up  by  the  automobile 
plowing  through  the  air.  That  the  binder  of  the  road  was  being 
destroyed  and  removed  was  perfectly  obvious;  the  cause  of  this  dis- 
integration, however,  was  not  immediately  understood. 

Cause  of        It  has  now  been  established  that  the  destruction  of  macadam  roads 

destruction   is  the  result  of  crushing  forces  which  are  in  excess  of  the  compressive 

of   strength  of  the  binder.      With  the  high  unit  loads  imposed  by  mod- 

macadam   ern  vehicles  upon  the  road  surface,  the  binder  is  crushed  and  the 

large  stones,  being  no  longer  bound  together,  are  pounded  into  the 

sub-grade  and  ruts  are  developed;  the  loosened  binder  meanwhile  is 

swept  away  by  each  passing  vehicle  and  breeze. 

The  destruction  of  this  type  of  road,  then,  is  due  primarily  to 
its  lack  of  strength.  Without  this  important  attribute  the  body  of 
the  road  cannot  distribute  the  loads  over  the  sub-grade,  and  each 
imperfection  and  irregularity  of  the  sub-grade  is  soon  reflected  upon 
the  surface  of  the  road. 

Rigid       A  sub-grade,  however  well  prepared,  is  far  from  having  a  homo- 
foundation  geneous  character.     Almost  invariably  it  is  in  a  cut  or  a  fill  and 
necessary  will  settle  unevenly.     If  then,  a  smooth  road  surface  is  to  be  main- 
tained, the  body  of  the  road  must  be  composed  of  a  rigid  material 
which  will  equalize  the  irregularities  of  the  sub-grade. 

Portland  cement  concrete  is  the  only  material  that  we  possess 
which  is  endowed  with  sufficient  compressive  and  tensile  strength 
to  fulfill  the  modern  requirements  of  a  road  material 


GOOD  CONCRETE  133 


The  development  of  the  sheet  asphalt  pavement  clearly  illus- 
trates this  fact.  Attempts  which  were  once  made  to  cover  a  non- 
rigid  road  foundation  with  a  wearing  surface  of  asphalt  were  never 
successful,  and  today  it  is  invariably  constructed  upon  a  foundation 
of  Portland  cement.  The  acknowledged  supremacy  of  this  type  of 
pavement  for  city  streets  is  to  be  attributed  to  the  rigidity  of  the 
concrete  base  and  its  ability  to  distribute  the  loads  over  ihe  sub-grade. 

This  fact  has  long  been  under  observation  by  highway  engineers 
and  its  adaptation  to  country  road  building  was  only  deferred  by 
the  high  cost  of  Portland  cement  which  prevailed  until  four  or  five 
years  ago.  About  five  years  ago  concrete  roads  were  constructed 
simultaneously  in  at  least  eight  different  States;  the  data  obtained 
from  the  observation  of  these  first  roads  is  largely  responsible  for  the 
present  enormous  extension  of  the  use  of  cement  in  highway  making. 

There  is  as  yet  no  general  single  standard  for  the  construction 
of  concrete  roads.  Three  types,  each  of  which  has  its  advocates, 
are  in  general  use. 

One-course  concrete, 
Two-course  concrete, 

One-course  concrete  with    a    wearing    surface 
of  bituminous  material. 

In  this  form  of  construction  only  one  layer  of  concrete  is  placed  One-course 
directly  upon  the  properly  prepared  sub-grade.     The  total  thickness  concrete 
of  the  concrete  after  compacting  is  somewhere  about  seven  inches. 

In  this  type  of  construction  an  adequate  base  of  concrete  is  first   Two-course 
placed,  followed  by  a  wearing  surface  of  richer  concrete  from  two  concrete 
to  three  inches  in  thickness.    A  wearing  surface  of  cement-sand-mortar 
has  not  been  found  to  give  satisfactory  results  and  its  use  has  been 
abandoned. 

In  this  type  of  construction,  which  seems  peculiarly  adapted  to  One-course 

Pacific  Coast  conditions,  a  layer  of  concrete,  the  thickness  of  which  concrete  with  a 

is  usually  controlled  by  local   conditions,  is  placed  on  a  properly  bituminous 

prepared  sub-base  and  covered  with  a  wearing  surface  of  bitumen  wearing  surf  ace 


114 GOOD  CONCRETE 

and  sand  from  Yi,"  to  f£"  in  thickness.  This  class  of  road  has  been 
adopted  by  the  State  Highway  Commission  and  by  the  Los  Angeles 
County  Highway  Commission.  Each  of  these  types  gives  excellent 
service.  There  are,  however,  a  number  of  factors  for  and  against 
each,  which  should  be  carefully  considered  before  deciding  what  type 
will  best  serve  a  given  purpose. 

Quality  oj  The  all-concrete  road,  when  properly  constructed,  gives  a  wearing 
concrete  surface  that  is  the  last  word  for  hardness  and  toughness.  Such  a 
necessary  surface,  however,  requires  careful  and  elaborate  provision  for  the 
protection  of  the  edges  of  the  expansion  and  shrinkage  joints.  Again, 
provision  must  be  made  for  the  eventual  wearing  out  of  the  concrete 
surface.  Careful  measurements  indicate  that  concrete  will  wear  down 
at  the  rate  of  1  / 1  6"  per  year,  so  that  a  2 "  surface  finish  will  have 
a  life  of  thirty-two  years.  Owing  to  the  serious  problem  involved 
in  bonding  a  new  wearing  surface  upon  an  old  concrete  base,  perhaps 
the  best  practice  will  be  to  replace  the  wornout  concrete  surface  with 
a  bituminous  wearing  surface. 

It  is  an  important  fact  to  remember  that  a  concrete  road  of  whatever 
type  affords  a  permanent  foundation  upon  which  any  form  of  wearing 
surface  may  be  placed  after  the  original  surface  dressing  is  worn  out. 

FUNDAMENTAL  REQUISITES  FOR  CONCRETE  ROAD  CONSTRUC- 
TION. 

In  applying  concrete  to  the  construction  of  roads  and  highways 
the  cardinal  point  is  to  fully  realize  what  demands  will  be  made  upon 
thp  material. 

Strength  in  concrete  is  a  matter  of  degree ;  it  can  be  varied  between 
wide  limits  at  will.  The  toughness  and  resistance  to  abrasion  can 
likewise  be  controlled  by  the  selection  of  a  properly  endowed  coarse 
aggregate. 

Wear  of       In  the  construction  of  concrete  roads  the  engineer  should  and  must 
concrete  be  satisfied  only  with  the  very  best  concrete  that  can  be  produced  from 
roads  the  materials  at  his  command. 


GOOD  CONCRETE 115 

If  one  considers  the  infinite  pains  and  attention  to  detail  expended 
in  the  proportioning  of  such  a  low-priced  commodity  as  sheet  asphalt, 
there  certainly  can  be  no  excuse  offered  for  the  loose  methods  of  pro- 
portioning, mixing  and  placing  concrete  now  in  general  use. 

With  a  given  specification  the  production  of  good  concrete  is  not  a 
matter  of  additional  expense,  but  simply  one  of  intelligence. 

In  the  construction  of  concrete  roads  the  factors  that  make  for  per- 
manence will  be: 

1.  A  sub-grade  well  rolled,  compacted  and  drained. 

2.  A  concrete  which  has  a  mortar  of  sufficient  strength  to  prop- 

erly bind  the  coarse  aggregate  together  and  enable  it  to 
resist  the  shock  and  wear  of  the  traffic. 

3.  A  coarse  aggregate  that  is  tough,  durable,  clean  and  entirely 

free  from  all  soft  or  decomposed  particles. 

4.  All  the  wear  is  to  be  taken  by  the  coarse  aggregate,  and  the 

mortar  shall  serve  only  to  rigidly  hold  the  coarse  particles 
in  place. 

5.  Methods  of  placing  and  curing  the  concrete  which  will  be 

such  as  to  permit  the  concrete  hardening  to  the  best  ad- 
vantage. 

6.  Adequate  provision  for  taking  care  of  shrinkage  and  expan- 

sion and  the  proper  protection  of  all  such  joints  to  prevent 
frazzling. 

PROVIDING  FOR  EXPANSION. 

The   question  of  providing   for  shrinkage   and   expansion   is   one   Expansion 
for  which  there  seems  to  be  more  than  one  solution.   It  is  now  a  ana 
well-established  fact  that  average  concrete  has  about  the  same  co-  Shrinkage 
efficient  of  expansion  for  every  degree  of  change  in  temperature  as 
steel  has;  but  aside  from  these  changes  in  volume,  due  to  changes 
in    temperature,    we   have   the    changes    in   volume    due    to    normal 
shrinkage  and  expansion.     Concrete  which  is  hardening  under  water 


116 GOOD  CONCRETE 

or  in  a  damp  environment  expands  constantly  up  to  a  certain  point. 
This  expansion,  due  to  hardening  in  water,  or  in  a  moist  environment, 
will  amount  to  0. 1 "  for  every  hundred  feet  at  the  end  of  two  years. 

When  concrete  is  allowed  to  harden  in  air,  or  in  a  dry  environment, 
a  contraction  or  shrinkage  takes  place,  which  amounts  for  a  1:2:4 
concrete  to  0.3"  for  every  hundred  feet  at  the  end  of  two  years. 
The  amount  of  this  expansion  and  shrinkage  is,  however,  greatly 
influenced  by  the  amount  of  water  used  in  mixing.  An  extremely 
wet  mixture  will  show  more  shrinkage  in  air  than  one  that  is  just 
about  plastic.  It  will  also  be  influenced  by  the  amount  of  sand 
present  in  a  concrete.  An  oversandsd  concrete  will  always  shrink 
more  than  a  properly  balanced  one. 

EXPANSION  AND  CONTRACTION  DUE  TO  CHANGES  IN  TEM- 
PERATURE. 

The  co-efficient  of  expansion  of  average  1:2:4  concrete  is 
.0000055,  which  can  very  conveniently  be  remembered  as  "five 
naughts  and  a  five,"  so  that  for  every  50  deg.  F.  rise  or  fall  in 
temperature  this  change  will  amount  to  about  1  /3"  per  hundred 
feet;  so  that  shrinkage  in  air  during  hardening  is  just  about  equal 
to  the  expansion  due  to  a  change  of  50  deg.  in  temperature.  It  is 
upon  this  fact  that  some  engineers  advocate  laying  the  concrete  road 
without  any  provision  for  either  expansion  or  contraction.  As  we 
have  shown  above,  there  is  a  theoretical  justification  of  this  attitude, 
but  in  allowing  nature  to  provide  its  own  reliefs  for  changes  in  vol- 
ume she  will  not  usually  produce  these  reliefs  in  geometrical  lines. 
The  cracks  may,  and  are  likely  to  be,  very  irregular.  Instead  of 
traversing  the  road  at  right  angles  to  its  length,  they  are  just  as 
likely  to  form  partly  at  light  angles  and  partly  in  the  same  direction 
as  the  length  of  the  road.  A  crack  parallel  to  the  line  of  traffic  will 
receive  more  wear  than  one  at  right  angles  to  it.  If  the  concrete 
surface  is  supplied  with  a  bituminous  wearing  surface,  it  will  be  a 
matter  of  indifference  in  what  direction  these  cracks  are  formed; 
but  if  the  road  is  to  be  supplied  with  a  concrete  wearing  surface,  the 


GOOD  CONCRETE  H7 

matter  of  making  provision  for  expansion  and  shrinkage  becomes  a 
very  vital  one.  The  first  all-concrete  roads  built  have  demonstrated 
the  fact  that  the  life  of  a  road  will  depend  upon  the  provision  for 
expansion  and  shrinkage  and  the  protection  of  these  joints.  The 
proper  protection  of  these  joints  adds  materially  to  the  cost  of  con- 
struction. 

Perhaps  the  most  satisfactory  method  yet  devised  is  that  used  in 
Wayne  County,  Mich.  The  joint  is  protected  by  a  patented  steel 
plate  called  the  Baker  plate,  which  is,  in  substance,  a  curved  steel 
plate  conforming  to  the  crown  of  the  road,  which  protects  both 
sides  of  the  expansion  joint  and  is  separated  by  either  several  layers 
of  tarred  paper  or  by  a  bituminous  compound.  These  plates  wear 
uniformly  with  the  concrete  and  do  much  to  prevent  the  formation 
of  little  irregularities  at  each  expansion  joint. 

THE  PROPER  INTERVAL  FOR  EXPANSION  JOINTS. 

The  amount  of  expansion  which  can  produce  cracks  will  vary  Interval  for 
with  the  season  of  the  year  in  which  the  concrete  is  laid.     If  concrete  expansion  and 
is  laid  in  Summer,  the  development  of  expansion  cracks  will  be  very  shinkage 
small,  because  the  concrete  is  at  its  maximum  volume  on  account  of  joints 
the  heat.     In  such  work  contraction  cracks  will  inevitably  develop. 
The  interval  at  which  relief  is  provided  varies  from  25  to  75  feet. 
This   holds   only   for  roads  with   concrete  wearing  surfaces.      The 
Los  Angeles  highway  engineers,  as  well  as  the  highway  engineers 
of   the   State  of   California,   who   have   adopted  as   their   standard 
the   one-course   concrete   road   with   a   bituminous   wearing   surface, 
make  no  provision  for  either  expansion  or  contraction,  as  the  wearing 
surface  will  automatically   flow  into   and  take  care  of  any   cracks 
that  are  formed. 

The  specifications  for  concrete  roadways  of  Wayne  County, 
Mich.,  require  an  expansion  joint  for  each  25  feet.  Those  of  Mason 
City,  la.,  one  every  37J/2  feet;  the  Illinois  Highway  Commission 
require  one  every  50  feet,  while  those  of  the  Maryland  State  High- 
way Commission  require  one  every  60  feet.  In  all  of  the  cases  above 


118  GOOD  CONCRETE 

cited  the  roads  are  all  provided  with  a  concrete  wearing  surface. 
The  proper  interval  for  any  locality  will  depend  upon  local  condi- 
tions and  is  one  that  the  engineer  will  have  to  determine  for  himself. 

How  MUCH  CROWN  FOR  CONCRETE  ROADS? 

There  can  be  no  argument  against  crowning  a  macadam  road, 
as  in  this  type  of  construction  the  life  of  the  road  depends  upon  its 
being  rapidly  and  well  drained.  Concrete,  on  the  other  hand,  when 
properly  made,  is  an  impermeable  material  whose  strength  is  not 
impaired  by  contact  with  water. 

The  matter  of  crown  and  its  degree  will  be  of  minor  importance 
in  a  concrete  road,  and  need  only  be  such  as  will  make  travel  in 
wet  weather  more  convenient,  by  permitting  the  drainage  to  take 
place  laterally  instead  of  longitudinally. 

Flatter        There  certainly  can  be  no  justification  for  adherence  to  the  old 
crown  for  precedents   established   for   the  water-bound   macadam   roads   when 
concrete   it  comes  to  crowning  a  concrete  road.     It  is  now  generally  recognized 
roads   that  a  concrete  road  needs  less  crown  than  does  a  water-bound  mac- 
adam one — in   fact,  some  constructors  prefer  to  give   the   road  no 
crown  at  all,  simply  building  the  surface  as  an  inclined  plane  sloping 
in  one  direction  only. 

The  crown  need  not  be  in  the  form  of  an  arc  of  a  circle,  but  can 
be  composed  of  two  planes  sloping  to  each  side  from  the  center. 

Excessive  crowns  in  concrete  roads  are  a  fruitful  source  of  longi- 
tudinal cracks.  Such  excessive  crowns  have  the  additional  disad- 
vantage that  they  concentrate  all  the  traffic  at  the  center  of  the  road, 
while  a  flatter  crown  distributes  the  traffic  over  the  entire  surface, 
thus  providing  a  uniform  wear.  The  crown  of  the  sub-grade  is 
usually  made  to  conform  to  that  of  the  finished  road  surface.  The 
crowns  for  concrete  roads  vary  from  J/g"  to  ^4"  Per  ft-  of  width. 

CONCRETE. 

Proportioning       Whatever  type  of  concrete  road  a  community  may  decide  upon. 
the  concrete  attention  to  the  proportioning,  mixing  and  placing  of  the  concrete  will 


GOOD  CONCRETE  119 

be  the  cardinal  point.  We  have  already  made  mention  of  the  neces- 
sity of  proportioning  and  making  a  concrete  of  such  physical  proper- 
ties as  will  resist  the  unusual  wear  to  which  the  work  will  be  subjected. 
The  sand,  first  of  all,  must  be  clean — it  need  not  be  sharp.  The 
word  "sharp"  in  specifications  for  sand  is  a  relic  of  Mediaevalism. 
The  sand  will  need  as  much  attention  to  determine  its  quality  as  will 
the  cement.  We  have  already  considered  in  the  chapter  dealing  with 
sand  and  its  physical  properties  the  various  items  which  determine 
the  quality  of  a  sand.  Perhaps  the  safest  and  most  expedient  way 
of  testing  sand  will  be,  first  of  all,  a  determination  of  the  amount  of 
silt,  and,  secondly,  its  tensile  strength.  For  the  purpose  of  road  con- 
struction the  sand  used  with  a  concrete  shall  show  a  tensile  strength 
in  pounds  per  square  inch  not  less  than  the  tensile  strength  of  the 
same  proportion  of  standard  Ottawa  testing  sand  when  made  up 
according  to  standard  methods  and  tested  with  the  same  cement  to 
be  used  on  the  work. 

The  coarse  aggregate  must  be,  first  of  all,  composed  of  a  tough  Coarse 
and  durable  rock  perfectly  free  from  any  soft  or  disintegrated  parti-  aggregate 
cles.     The  rock  is  depended  upon  to  take  the  wear  of  the  traffic, 
and  if  there  are  soft  places,  these  will  be  worn  away  in  a  short  time 
and  leave  a  cavity  in  the  surface  which  becomes  the  nucleus  for  wear, 
and  a  rut  will  soon  result — in  much  the  same  manner  as  one  soft 
brick  in  many  hard  bricks  in  a  brick  pavement  will  start  the  destruc- 
tion of  such  a  type  of  wearing  surface. 

The  coarse  aggregate  may  be  either  a  crushed  rock  or  screened 
gravel.  Gravel  is  usually  composed  of  the  toughest  particles  of  rock 
which  have  resisted  erosion.  They  represent  the  most  refractory  por- 
tion of  the  rock  from  which  they  were  derived.  Natural  screened 
gravl,  however,  will  sometimes  carry  quite  a  proportion  of  shale 
boulders,  which  would  unfit  them  for  the  intended  use. 

The  proportion  of  cement  to  total  aggregate  should  never  be  less  Proportioning 
than    1 :6.      Perhaps  the  most  glaring  defect  that  one  finds  in  the  concrete 
majority  of  specifications  is  the  arbitrary  fixing  of  the  proportion  of 
sand  to  rock.     For  example:  A  1  :6  mixture  is  usually  construed  as 


120 GOOD  CONCRETE 

meaning  one  part  of  cement,  two  parts  of  sand  and  four  parts  of 
rock.  This  may  be  the  best  proportion  of  sand  to  rock  for  some 
mixtures.  The  scientific  way  of  determining  the  best  and  strongest 
mixture  would  be  by  the  volumetric  synthetic  method,  as  explained 
on  page  39.  Bearing  in  mind  that  that  combination  of  sand  and 
coarse  aggregate  for  a  fixed  proportion  which  gives  with  a  fixed 
amount  of  cement  the  smallest  volume  of  plastic  concrete  will  be  the 
strongest  and  densest  mixture. 

It  would  be  well  at  this  point  to  emphasize  that  the  strength  of  a 
concrete  depends  upon  the  strength  of  its  cement  and  sand  mortar. 
The  tendency  is,  if  a  concrete  does  not  work  smooth  enough  in 
laying,  to  add  more  sand.  In  doing  this  the  constructor  is  deliber- 
ately weakening  his  concrete.  It  apparently  never  occurs  to  him 
that  the  proper  thing  to  do  would  be  to  decrease  the  rock- 

DETERMINING  THE  BEST  PROPORTION  OF  SAND  AND  ROCK  BY 
THE  VOLUMETRIC,  OR  CYLINDER  METHOD. 

If,   for  example,  the  specified  proportion  of  cement  to  aggregate 
is  fixed  as    1  :6,  the  procedure  would  be  as  follows:     Construct  a 
cylinder  about  6"  in  diameter,  plugged  at  one  end,  and  mark  on  a 
stick  the  inside  clear  depth  of  this  cylinder.     Divide  this  length  into 
as   many   equal   divisions   as   there   are   parts   of   cement   and   total 
aggregate.     For  a  1  :6  mix  the  distance  on  this  stick  would  be  divided 
into  seven  equal  parts.     Then  measure  by  means  of  this  stick  various 
proportions  of  sand  and  coarse  aggregate,  such  as,  for  example: 
1  part  of  cement,  1 J/2  parts  of  sand  and  41/2  parts  of  rock 
1  part  of  cement,  2       parts  of  sand  and  4       parts  of  rock 
Convert  each  mixture   into  a  plastic  concrete   and  ram  it  into  the 
cylinder.     Then  that  mixture  which  gives  the  smallest  volume  will 
be   the  proper   mixture  to   use.      For   further  details   the   reader   is 
referred  to  the  chapter  on  Proportioning  Concrete. 

Mixing  The  logical  way  to  mix  concrete  is  to  first  prepare  the  sand  and 
cement  mortar  of  proper  consistency,  and  to  add  to  it  the  wet  aggre- 
gate. In  machine  mixing  this  is  done  without  any  inconvenience 


GOOD  CONCRETE 121 

whatsoever.  The  sand  and  cement  are  charged  into  the  mixing 
machine  and  the  machine  allowed  to  make  several  revolutions.  The 
water  is  then  added,  and  as  soon  as  the  mortar  becomes  uniformly 
mixed  the  rock  or  coarse  aggregate  is  charged  into  it.  By  this  method 
of  mixing  much  is  done  to  obviate  the  tendency  of  a  concrete  to 
draw  crack — that  is,  to  open  up  into  short  parallel  cracks.  These 
cracks  are  due  to  the  cement  absorbing  water  from  the  sand.  A 
cement  particle,  as  minute  as  it  is,  is  a  very  hard  and  refractory 
material.  It  needs  a  certain  definite  time  to  soften  in  contact  with 
water,  and  if  it  is  not  allowed  this  time  it  will  do  so  after  it  is  placed 
into  the  work  and  give  the  concrete  the  appearance  of  "setting  up." 

The  sub-grade  upon  which  the  concrete  is  to  be  deposited  must  be  Depositing 
saturated  with  water,  otherwise  the  concrete  will  be  robbed  of  the   the  concrete 
water  which  is  so  essential  to  its  proper  hardening. 

The  concrete,  after  it  is  in  place,  must  be  protected  from  direct  Protection 
sunlight  and  draft.     The  practice  in  the  Middle  Western  States  is  to   of  the 
cover  the  freshly  laid  concrete,  as  soon  as  it  has  taken  initial  set,   concrete 
with  a  large  canvas.     This  canvas  is  allowed  to  remain  for  1 2  to  24   Qjtcr 
hours,  after  which  the  surface  of  the  concrete  is  thoroughly  wet  and 
kept  wet  for  seven  days.     Where  a  sand  or  other  proper  material 
is  available,  it  may  be  placed  on  the  wetted  concrete  surface  and 
saturated  with  water.     If  the  road  surface  is  to  be  finished  with  a 
bituminous  wearing   surface,   the   properly   cured   concrete   must   be 
thoroughly  cleaned  and  dried  before  the  oil  and  sand  can  be  applied. 


\22 


GOOD  CONCRETE 


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Specifications 

for 
Concrete  Roads 

with 

Asphaltic  Oil 
Wearing  Surface 


CHAPTER  VIII. 


SPECIFICATIONS  OF  THE  CITY  OF  GLENDORA 

For  the  Construction  of 

PORTLAND  CEMENT  CONCRETE  PAVEMENT 

WITH  ASPHALTIC  OIL  WEARING  SURFACE, 

By 

FLOYD  G.  DESSERY. 

The  work  herein  provided  for  is  to  be  done  in  accordance  with  Genera/ 
the  plans,  profiles,  detail  drawings  and  cross-sections  for  the  work  requirements 
on  file  in  the  office  of  the  City  Engineer  of  the  City  of  Glendora, 
and  all  work  shall  during  its  progress  and  on  its  completion,  conform 
to  the  lines  and  levels  which  may  from  time  to  time  be  given  by  said 
City  Engineer. 

( 1  )      To  excavate  or  fill  in  the  area  upon  which  the  pavement  The  work 
herein  provided  for  is  to  be  constructed  on  the  Street,  Avenue,  Alley  to  be  done 
or  Roadway,  to  such  extent  as  may  be  required  by  the  plans,  profiles,  is  as  follows. 
detail  drawings  and  cross-sections  and  these  specifications. 

(2)  To    construct    and    lay   thereon    the   pavement    hereinafter 
specified. 

(3)  To   furnish   all  materials  and  labor  necessary  to  perform 
said  work  and  construct  the  same. 


126 GOOD  CONCRETE 

(4)  And  to  do  whatever  else  is  required  by  these  specifications 
to  be  done. 

Sub-grade  The  surface  of  the  compacted  sub-grade  for  the  roadway  shall  be 
such  distance  below  the  finished  surface  of  the  Street,  Avenue,  Alley 
or  Roadway  as  shown  on  the  above  mentioned  plans,  profiles,  detail 
drawings  or  cross-sections. 

Grading  Grading  shall  include  the  removal  of  all  earth,  stone,  loose  rock, 
cement,  hardpan,  boulders,  solid  rock  and  all  other  materials  which 
may  be  encountered  in  preparing  the  sub-grade,  and  shall  include  also 
all  filling,  trimming,  shaping,  packing  down,  refilling,  surfacing,  roll- 
ing or  other  work  which  may  be  necessary  in  bringing  the  surface  of 
the  roadway  to  the  required  sub-grade.  When  required  by  the  plans, 
profiles,  details  drawings  or  cross-sections,  the  area  back  of  the  curb 
line  shall  be  graded  to  conform  to  the  grade  shown  on  the  said 
plans,  profiles,  detail  drawings  or  cross-sections. 

When  mud,  sand,  vegetable,  or  other  soft  material  is  encountered, 
it  shall  be  removed  to  a  depth  of  twelve  (12)  inches  below  sub-grade, 
and  the  space  filled  with  good  gravel  or  earth,  which  shall  be  rolled 
with  a  self-propelled  road  roller  weighing  not  less  than  ten,  (10) 
tons,  until  the  surface  of  the  foundation  ceases  to  sink  under  or 
creep  in  front  of  the  roller. 

In  places  where  filling  is  necessary  to  bring  the  street  to  the  re- 
quired grade  or  sub-grade,  all  brush  and  rubbish  shall  be  removed 
and  the  fill  shall  be  made  with  good  sound  earth.  The  embankment 
shall  be  carried  up  of  full  width  in  layers  not  to  exceed  one  ( 1 ) 
foot  in  thickness,  and  the  teams  shall  be  made  to  travel  as  evenly 
as  possibly  over  the  whole  surface  of  each  layer,  both  coming  and 
going. 

If  there  should  be  an  excess  of  smooth  or  rounded  stone,  rock  or 
boulders  in  or  upon  the  material  forming  the  sub-grade,  the  same  shall 
be  removed  and  good  earth  or  gravel  shall  be  substituted  in  place 
thereof. 


GOOD  CONCRETE 127 

The  formation  of  well-defined  ruts  is  especially  prohibited.  No 
material  of  spongy  nature  shall  be  used  in  filling. 

After  each  block  or  section  has  been  graded  as  above  specified  the 
surface  shall  be  thoroughly  watered,  and  shall  then  be  rolled  with 
a  self-propelled  road  roller  weighing  not  less  than  ten  (10)  tons, 
until  the  surface  is  smooth  and  unyielding. 

Depressions  made  by  rolling  shall  be  leveled  up  with  good  earth, 
thoroughly  sprinkled  and  rolled  again.  Such  portions  of  the  street 
as  cannot  be  reached  by  the  roller,  and  all  places  excavated  below 
the  sub-grade  and  refilled  and  all  pipe  trenches  and  other  places 
which  cannot  be  properly  compacted  by  the  roller,  shall  be  tamped 
solid,  and  in  case  of  wet  weather  or  soft  and  muddy  ground  making 
the  use  of  the  roller  unsafe  or  impracticable,  the  rolling  shall  not  be 
undertaken  until  the  ground  has  become  sufficiently  dry.  The  surface 
of  the  compacted  sub-grade  shall  be  so  finished  that  it  will  not  vary 
at  any  point  more  than  one-half  ( Yi )  inch  from  its  intended  position. 
The  Contractor  shall  notify  the  Street  Superintendent  when  the  sub- 
grade  shall  have  been  prepared  as  above  specified  and  no  further 
work  shall  be  done  upon  it  until  it  has  been  examined  and  a  certificate 
of  acceptance  has  been  issued  by  said  Street  Superintendent. 

Upon  the  sub-grade  prepared  as  above  specified  shall  be  laid  a  Concrete 
concrete  foundation  of  the  thickness,  width  and  form  shown  on  the   foundation 
plans,  profiles,  detail  drawings  or  cross-sections. 

Proportions:  The  cement  concrete  shall  be  composed  of:  One  Concrete 
(1)  part  of  Portland  Cement,  Two  (2)  parts  of  sand  or  broken 
stone  screenings,  and  Four  (4)  parts  coarse  gravel  or  broken  stone. 
Gravel,  broken  stone  or  crushed  rock  forming  the  coarse  aggregate 
shall  not  exceed  in  its  greatest  dimension  three- fourths  (24)  of  the 
thickness  of  the  concrete  foundation  to  be  constructed. 

Measuring  and  Mixing:  All  proportions  shall  be  obtained  by 
actual  measurement  in  boxes  and  no  material  shall  be  used  which 
has  not  been  thus  measured.  All  mixing  shall  be  done  in  suitable 
boxes  or  upon  tight  platforms  or  in  mixers  of  an  approved  type.  In 


128  GOOD  CONCRETE 

the  process  of  mixing  the  concrete,  the  broken  stone,  gravel  or  coarse 
aggregate  shall  be  spread  in  a  regular  layer  not  over  ten  (10)  inches 
in  depth  on  the  platform;  upon  this  coarse  aggregate  shall  be  uni- 
formly spread  the  proper  amount  of  sand  or  fine  aggregate;  and  upon 
the  fine  aggregate  shall  be  spread  the  required  amount  of  cement. 
The  whole  mass  shall  then  be  mixed  by  turning  at  least  three  (3) 
times  dry,  sufficient  water  shall  then  be  added  in  a  fine  spray  to  pro- 
duce a  concrete  of  a  consistency  which  will  require  light  tamping 
to  flush  mortar  to  the  surface,  after  which  the  whole  mass  shall  be 
turned  two  (2)  times  wet. 

If  a  machine  is  used  for  mixing,  it  must  be  of  a  standard  or  ap- 
proved type  and  the  concrete  so  mixed  shall  be  at  least  equivalent 
to  that  mixed  by  hand,  as  above  described.  No  concrete  shall  be 
used  that  shows  evidence  of  having  set  or  that  has  become  unfit  for 
good  work  from  standing  too  long  or  from  any  other  cause,  and  no 
remixing  of  concrete  will  be  allowed. 

Placing  After  the  concrete  has  been  mixed  as  above  specified,  it 
shall  be  handled  rapidly  and  successive  batches  deposited  in  a  con- 
tinuous operation  completing  each  individual  section.  Under  no 
circumstances  shall  more  than  thirty  (30)  minutes  elapse  between 
the  mixing  and  placing  of  the  batch  of  concrete. 

The  upper  surface  of  the  concrete  shall  be  finished  parallel  to  and 
three  eighths  ( ^ )  of  one  ( 1  )  inch  below  the  grade  of  the  finished 
pavement  by  thoroughly  hand  tamping  until  the  mortar  flushes  freely 
to  the  surface.  After  the  concrete  has  been  thoroughly  tamped,  it 
shall  be  immediately  brought  to  a  smooth  and  even  surface  by  the 
use  of  a  flexible  wood  float  formed  to  truly  fit  the  curve  of  the  crown 
and  extending  entirely  across  the  pavement,  after  which  no  disturb- 
ance of  any  character  of  the  surface  will  be  allowed.  The  earth 
foundation  or  sub-grade  shall  be  thoroughly  sprinkled  immediately 
before  placing  the  concrete. 

All  concrete  shall  be  placed  at  once  after  mixing.  As  soon  as 
the  surface  of  the  concrete  has  been  finished  as  above  specified  it 


GOOD  CONCRETE 129 

shall  be  protected  from  the  direct  rays  of  the  sun  and  from  rain  and 
wind  by  spreading  a  wetted  canvas  over  it.  The  canvas  shall  be 
allowed  to  remain  at  least  ten  (10)  hours  over  the  fresh  concrete, 
during  which  time  it  shall  be  sprinkled  at  least  once,  after  which 
time  the  canvas  shall  be  removed  and  the  surface  of  the  concrete  shall 
be  sprinkled  with  a  spray  (and  not  a  jet)  of  water  at  intervals  of 
not  exceeding  three  (3)  hours  between  each  application  of  water. 
This  sprinkling  shall  continue  over  a  period  of  not  less  than  ten  (10) 
hours,  after  which  the  surface  of  the  concrete  shall  be  covered  with 
a  layer  of  earth  or  soil  to  a  depth  not  less  than  one  ( 1  )  inch  when 
wetted  and  compacted.  The  earth  or  soil  covering  shall  then  be 
immediately  sprinkled  until  water  runs  from  all  the  surface.  This 
manner  of  sprinkling  shall  be  performed  at  least  three  (3)  times  each 
day  and  continue  for  fourteen  (14)  days  after  the  placing  of  the 
concrete.  No  traffic  of  any  nature  whatever  shall  be  permitted  to 
pass  over  the  concrete  for  a  period  of  thirty  (30)  days  after  the 
concrete  has  been  placed. 

Expansion  and  contraction  joints  shall  be  constructed  in  accord-  Expansion 

ance  with  and  where  shown  on  the  plans,  profiles,  detail  drawings  or  and 

cross-sections.     They  shall  be  carefully  contructed  and  where  templets  contraction 

are  used  to  form  the  joints,  the  templets  shall  be  removed  in  such  a  joints 
manner  that  will  not  break,  crack  or  injure  the  edges  of  the  concrete 
forming  the  joint. 

The  filler  for  joint  space  formed  by  the  removal  of  the  templets 
shall  be  made  with  the  same  material  that  composes  the  wearing  sur- 
face hereinafter  described.  This  space  or  joint  to  be  filled  shall  be 
filled  prior  to  the  application  of  any  asphaltic  oil,  screenings  or  sand 
to  the  surface  of  the  concrete  and  care  shall  be  exercised  that  the 
screenings  or  sand  and  asphaltic  oil  are  well  mixed  and  incorporated 
and  that  no  surplus  asphaltic  oil  or  sand  shall  be  applied,  but  after 
properly  filling  the  space  or  joint  the  top  of  the  same  shall  be  level 
with  the  top  or  surface  of  the  concrete  base.  When  required  by  the 
plans,  profiles,  detail  drawings  or  cross-sections,  joints  extending  the 
full  length  of  the  roadway  shall  be  constructed.  These  joints  extend- 


BO GOOD  CONCRETE 

ing  longitudinally  shall  be  formed  by  the  use  of  a  necessary  amount  of 
tarred  paper  (depending  on  the  thickness  of  such  paper)  to  make 
the  joints  conform  to  the  dimensions  shown  on  the  plans,  profiles,  de- 
tail drawings  or  cross  sections.  All  joints  shall  extend  through  the 
full  depth  or  thickness  of  the  concrete  and  shall  be  well  aligned 
and  made  in  a  neat  and  workmanlike  manner. 

Unless  otherwise  provided  for  in  the  plans,  profiles,  detail  drawing 
or  cross-sections,  the  portion  of  the  pavement  adjoining  the  curbs  and 
forming  the  gutters  shall  be  constructed  for  the  full  length  of  the 
work  before  any  other  portion  of  the  pavement  shall  be  constructed. 

Fofrm,  Forms  for  all  concrete  work  shall  be  free  from  warp,  or  other  de- 
fects and  of  sufficient  strength  to  resist  springing  out  of  line  when 
properly  staked,  they  shall  be  securely  staked  or  otherwise  held  to  the 
established  lines  and  grades  and  extend  to  the  full  depth  of  the  con- 
crete and  their  upper  edges  shall  conform  to  the  established  grade 
of  the  pavement.  All  wooden  forms  shall  be  thoroughly  wetted  or 
oiled  and  metal  forms  oiled  before  any  material  is  deposited  against 
them.  All  mortar  and  dirt  shall  be  removed  from  forms  which  have 
been  previously  used. 

Cement  The  cement  used  shall  be  Portland  Cement  and  shall  conform 
to  the  following  conditions  and  be  subject  to  the  following  tests:  The 
tests  shall  be  made  by  the  methods  and  under  the  conditions  pre- 
scribed by  the  committee  of  the  American  Society  of  Civil  Engineers 
and  shall  be  open  to  the  Contractor. 

Not  less  than  ninety-two  (92)  per  cent  of  the  weight  of  the  cement 
must  pass  through  a  sieve  of  one  hundred  ( 1 00)  meshes  to  the  inch 
and  not  less  than  seventy-five  (75)  per  cent  by  weight  must  pass 
through  a  sieve  of  two  hundred  (200)  meshes  to  the  inch. 

Time  of  Setting:  The  initial  set  of  the  cement  shall  be  in  not  less 
than  thirty  (30)  minutes  when  mixed  neat  with  the  smallest  possible 
amount  of  water  at  the  temperature  at  which  it  flows  from  the  tap 
in  the  testing  room  provided  ty  the  City  of  Glendora,  but  hard  set 


GOOD  CONCRETE  j3i 

must  develop  in  not  less  than  one  ( 1 )  hour  nor  more  than  ten  (10) 
hours. 

Tensile  Strength :  Briquettes  one  ( 1 )  inch  square  in  section  shall 
attain  at  least  the  following  tensile  strength  and  shall  show  no  retro- 
gression within  the  periods  specified:  After  twenty-four  (24)  hours 
in  moist  air  neat,  one  hundred  fifty  (150)  pounds  per  square  inch. 
After  seven  (7)  days  (Briquettes  to  remain  in  moist  air  one  (1) 
day,  in  water  six  (6)  days,  neat,  four  hundred  fifty  (450)  pounds 
per  square  inch:  three  (3)  parts  sand  to  one  (1)  part  cement,  one 
hundred  fifty  (1  50)  pounds  per  square  inch.  After  twenty-eight  (28) 
days  briquettes  to  remain  in  moist  air  one  ( 1  )  day,  in  water,  twenty- 
seven  (27)  days,  neat,  five  hundred  fifty  (550)  pounds  per  square 
inch,  three  (3)  parts  sand  to  one  (1)  part  cement,  two  hundred 
(200)  pounds  per  square  inch. 

Soundness:  Test  pats  of  neat  cement  about  three  (3)  inches  in 
diameter,  one-half  (Yz)  mch  thick  at  the  center  and  tapering  to  a 
thin  edge,  shall  be  kept  in  moist  air  for  a  period  of  twenty-four  hours. 
They  shall  then  be  exposed  in  a  steam  bath,  above  boiling  water, 
in  a  loosely  closed  vessel  for  five  (5)  hours.  At  the  expiration  of 
this  time,  the  pats  shall  remain  firm  and  hard  and  shall  show  no  signs 
of  distortion,  checking,  cracking  or  disintegrating.  Samples  of  the 
cement  proposed  to  be  used  upon  any  piece  of  work  shall,  upon  re- 
quest, be  furnished  to  the  City  Engineer  for  test,  and  any  cement  the 
samples  of  which  do  not  come  up  to  the  required  standard  shall  be 
immediately  and  permanently  removed  from  the  work. 

Fine  Aggregate:    The  fine  aggregate  shall  consist  of  an  approved  Sand, 
material  of  silicious,  granitic  or  igneous  origin,  hard,  durable  and  free  stone, 
from  mica  in  excess  of  five  (5)  per  cent  by  weight.     It  shall  be  free  screenings 
from  oil  or  organic  matter,  and  must  not  contain  more  than  six  (6)  and  broken 
per  cent  by  weight  of  clay,  silt  and  other  material  passing  a  No.  1 00  stone 
Standard  Sieve.     It  shall  all  pass  a  No.  4  Standard  Sieve,  and  at 
least  fifty  (50)  per  cent,  but  not  more  than  eighty-five  (85)  per  cent 
by  weight,  shall  be  retained  on  a  No.  30  Standard  Sieve. 


132  GOOD  CONCRETE 

Coarse       The  coarse  aggregate  shall  be  sound  gravel  or  broken  stone,  having 
aggregate  a  specific  gravity  of  not  less  than  2.6.     It  shall  be  clean  and  free 
from  all  foreign  matter,  uniformly  graded,  and  shall  range  in  size 
from  one-fourth  (!/*)  inch  up  to  three  (3)  inches. 

Water        The  water  used  in  mixing  the  concrete  shall  be  clean,  free  from  oil, 
acid,  alkalies  or  vegetable  matter  of  any  nature. 

Asphaltic       When  the  concrete  foundation  has  been  thoroughly  cleaned  of  all 
oil  tearing  dirt  by  sweeping  and  flushing  with  water  and  after  it  has  thoroughly 
surface  dried,  the  entire  surface  of  the  concrete  foundation  shall  be  covered 
with  heavy  asphaltic  oil  of  the  quality  hereinafter  specified.     The  oil 
shall  be  applied  under  pressure  by  means  of  an  approved  spraying 
machine,  at  the  rate  of  one-half  (|/2)  gallon  per  square  yard  of  sur- 
face covered. 

Immediately  after  the  asphaltic  oil  has  been  applied,  the  entire 
oiled  surface  shall  be  covered  with  a  thin  layer  of  broken  stone 
screenings  in  quantity  sufficient  to  absorb  the  oil.  Wherever  free  oil 
shows  on  the  surface,  additional  screenings  shall  be  applied  to  absorb 
the  oil. 

After  the  oil  applied  as  above  specified  has  been  covered  with 
screenings  for  at  least  three  (3)  days  the  entire  surface  shall  again 
be  covered  with  asphaltic  oil  of  the  quality  and  in  the  manner  above 
specified  at  the  rate  of  one-fourth  (J4)  gallon  per  square  yard  of  sur- 
face covered. 

Immediately  after  the  asphaltic  oil  has  been  applied  it  shall  be 
covered  with  a  thin  layer  of  broken  stone  screenings  or  coarse,  screened 
sand,  in  quantity  sufficient  to  absorb  the  oil,  and  wherever  free  oil 
shows  through  the  surface  of  screenings  or  sand  thus  applied  addi- 
tional screenings  or  sand  shall  be  applied  to  absorb  it.  The  surface  of 
the  roadway  thus  prepared  shall  be  maintained  for  at  least  ten  (10) 
days,  after  the  last  application  of  asphaltic  oil,  and  no  traffic  of  any 
nature  will  be  permitted  to  pass  over  it  until  the  expiration  of  such 
time. 

The  completed  pavement  shall  present  a  uniform  bituminized  ap- 
pearance, with  a  true  and  even  surface  free  from  irregular  patches 
of  screenings  or  excess  oil. 


GOOD  CONCRETE 


133 


No  gravity  machine  shall  be  used  in  applying  the  asphaltic  oil  and 
the  Contractor  shall  exercise  great  care  in  applying  the  oil  in  uniform 
quantity,  and  if  the  class  of  machine  or  apparatus  for  applying  the 
oil  is  such  that  the  curbs  will  become  spattered  or  coated  with  the  oil 
when  being  applied  to  the  pavement,  then  the  Contractor  shall  use 
such  means  as  may  be  necessary  to  prevent  the  oil  from  depositing 
on  the  curb  or  curb  face. 

No  asphaltic  oil  shall  be  applied  on  the  concrete  foundation 
until  at  least  twenty-one  (2 1  )  days  have  elapsed  after  the  concrete 
foundation  has  been  completed. 


Broken 
stone 

screenings  and 
sand  for 
asphaltic 
wearing  coal 


Broken  stone  screenings  shall  be  that  portion  of  crusher  run  that 
passes  through  a  circular  screen  opening  one-half  (j/2)  inch  in  diam- 
eter and  from  which  all  fine  dust  has  been  removed.  The  broken  stone 
screenings  shall  be  hard,  tough,  sound,  of  irregular  cleavage  and  of 
uniform  quality,  from  which  substantially  all  dust  has  been  removed. 

All  sand  shall  be  clean,  coarse  screened  sand,  all  of  which  will 
pass  through  a  circular  screen  opening  one-half  (J/2)  inch  in  diameter 
and  from  which  all  fine  sand  has  been  removed. 

Oil:     The  oil  shall  be  a  heavy  asphaltic  oil  prepared  from  Cali-    Asphaltic  oil 
fornia  products,  and  shall  be  free  from  admixtures  with  any  residues 
obtained  by  the  artificial  distillation  of  coal,  coal  tar  or  paraffine  oil 
and  shall  conform  to  the  following  requirements: 

Water:  It  shall  not  contain  more  than  one-half  (Yz)  of  one  (1  ) 
per  cent  of  water  by  volume. 

Sediment:  It  shall  not  contain  more  than  one-half  ('/z)  of  one 
( 1  )  per  cent  of  sediment  by  volume. 

Volatility:  When  twenty-five  (25)  grammes  placed  in  a  No.  13 
brass  spherical  dish,  with  a  radius  of  four  and  two-tenths  (4.2)  centi- 
meters, inside  measurement,  is  evaporated  in  a  Blackmar  or  Richard- 
son type  of  Asphalt  Oven,  maintained  at  a  uniform  temperature  of 
two  hundred  and  twenty  (220)  degrees  Fahrenheit  for  one  ( 1  )  hour, 
it  shall  not  lose  more  than  seven  tenths  (7-10)  of  one  ( 1  )  per  cent. 


134  GOOD  CONCRETE 

Solubility  In  Carbon  Di-Sulphide :  It  shall,  when  freed  from  water,  be  sol- 
uble to  at  least  ninety-nine  and  five-tenths  (99.5)  per  cent  in  pure 
carbon  di-sulphide. 

In  CS2  Bromine  Solution:  The  Bitumen  soluble  in  carbon  di- 
sulphide  shall  be  soluble  to  the  extent  of  at  least  ninety-nine  and 
eighty-five  one  hundredths  (99.85)  per  cent  in  a  solution  composed 
of  one  hundred  and  thirty-five  (135)  milligrams  of  bromine  to  one 
hundred  ( 1 00)  cubic  centimeters  of  carbon  di-sulphide,  when  twenty- 
five  (25)  cubic  centimeters  of  the  solution  are  poured  on  two  (2) 
grammes  of  the  oil  in  an  Erlenmeyer  Flask,  which  is  then  shaken  in 
the  dark  for  three  (3)  minutes,  the  solution  being  immediately  filtered 
through  a  Gooch  Crucible  using  a  suction  equal  to  a  column  of  mer- 
cury not  more  than  eight  (8)  inches  high. 

When  the  solution  has  all  passed  through  the  crucible,  the  crucible 
shall  be  washed  with  pure  carbon  disulphide,  dried  at  two  hundred 
and  twelve  (212.0)  to  two  hundred  and  twenty  (220.0)  degrees 
Fahrenheit  and  weighed. 

The  amount  of  bromine  in  the  carbon  di-sulphide  solution  is  deter- 
mined by  adding  to  twenty-five  (25.0)  Cubic  Centimeters  of  the  solu- 
tion, about  twenty-five  (25)  cubic  centimeters  of  water  and  an  excess 
of  Potassium  Iodide  crystals  and  then  titrating  by  decinormal  solution 
of  Sodium  Thio  sulphate. 

In  Casoline:  The  asphalt,  prepared  as  hereinafter  specified, 
having  a  penetration  between  seventy-five  (75.0)  and  eighty  (80.0) 
degrees  District  of  Columbia  Standard,  shall  be  soluble  in  California 
gasoline  (hereinafter  specified)  to  the  extent  of  at  least  eighty-five  and 
five-tenths  (85.5)  per  cent  when  one  hundred  and  fifty  (150.0) 
cubic  centimeters  of  gasoline  are  poured  on  five-tenths  (0.5)  of  one 
gramme  of  the  asphalt  in  solution  in  one  (1.0)  cubic  centimeter  of 
carbon  di-sulphide  and  shaken  ocasionally  for  ten  (10)  minutes. 
This  test  shall  be  made  at  about  77  degrees  Fahrenheit. 

Gasoline:  The  gasoline  herein  specified  shall  be  between  sixty 
(60.0)  and  sixty  and  six-tenths  (60.6)  degrees  Baume  at  60°  F. 


GOOD  CONCRETE  135 

Between  fifty-eight  (58.0)  and  sixty-one  (61.0)  per  cent  shall 
distill  and  pass  out  of  condenser  at  two  hundred  and  twenty-five 
(225.0)  degrees  Fahrenheit.  Not  less  than  three  (3.0)  nor  more 
than  four  (4.0)  per  cent  shall  remain  in  the  still  at  three  hundred  and 
thirty  (330.0)  degrees  Fahrenheit. 

The  rate  of  distillation  shall  be  not  less  than  one  (1.0)  nor  more 
than  two  (2.0)  drops  per  second.  The  amount  taken  for  test  shall 
be  two  hundred  and  fifty  (250.0)  cubic  centimeters. 

After  being  freed  from  water,  it  shall  contain  not  less  than  Asphalt 
ninety-five  (95)  per  cent  of  asphalt,  having  a  temperature 
of  seventy-seven  (77)  degrees  Fahrenheit  a  penetration  of  eighty 
(80.0)  degrees  District  of  Columbia  Standard.  The  percentage  of 
asphalt  shall  be  determined  by  heating  twenty-five  (25.0)  grammes 
in  a  No.  1 8  brass  spherical  dish  with  a  radius  of  four  (4.0)  and  two 
tenths  (0.2)  centimeters,  inside  measurement,  in  a  Blackmar  or  Rich- 
ardson type  of  oven  maintained  at  a  uniform  temperature  of  four 
hundred  and  thirty  (430.0)  degrees  Fahrenheit  until  it  has  reached 
the  proper  consistency,  when  the  weight  of  the  residuum  is  determined 
and  the  per  cent  calculated  (the  temperature  of  the  oven  shall  be 
taken  with  the  bulb  of  the  thermometer  resting  on  the  bottom  thereof). 

The  ductility  of  the  asphalt  as  above  prepared  having  a  Ductility 
penetration  between  seventy-five  (75.0)  and  eighty-five  (85.0)  de- 
grees District  of  Columbia  Standard  shall  be  not  less  than  one  hun- 
dred and  ten  ( 1  1 0.0)  centimeters.  This  test  to  be  made  by  im- 
mersing the  asphalt  in  water  which  is  kept  at  a  uniform  temperature  of 
seventy-seven  (77.0)  degrees  Fahrenheit  for  at  least  thirty  (30.0) 
minutes,  using  the  "Dow"  asphalt  mould  and  pulling  apart  at  a 
uniform  rate  of  speed  of  five  (5.0)  centimeters  per  minute. 

All  oil  shall  be  delivered  at  the  point  of  application  at  a  tempera-  Thermal 
ture  or  not  less  than  three  hundred  (300.O)  degrees  Fahrenheit,  nor  readings 
more  than  four  hundred  (400)  degrees  Fahrenheit. 


136 GOOD  CONCRETE 

Corrections  In  determining  the  quantity  of  oil  delivered  the  correction 
Thermal  for  expansion  of  heat  shall  be  as  follows:  From  the  meas- 
ured volume  of  oil  received  at  any  temperature  above  sixty 
(60.0)  degrees  Fahrenheit,  an  amount  equivalent  to  three-tenths 
(0.3)  of  one  (I)  per  cent  for  every  ten  (10)  degrees  above  said 
sixty  (60)  degrees  Fahrenheit  shall  be  subtracted  as  the  correction 
for  expansion  by  heat.  For  the  purpose  of  measuring  this  oil,  a  tem- 
perature of  sixty  (60)  'degrees  Fahrenheit  shall  be  deemed  normal 
temperature. 

All  of  the  oiling  hereinbefore  specified  shall  be  done  only  when 
the  atmospheric  temperature  is  above  sixty-five  (65)  degrees  Fahren- 
heit and  only  when  the  sun  is  shining.  No  oiling  shall  be  permitted 
unless  the  surface  to  be  covered  is  thoroughly  dry. 


SPECIFICATIONS  OF  THE  LOS  ANGELES  HIGHWAY 
COMMISSION. 

CONCRETE  PAVEMENT  WITH  BITUMINOUS  WEARING  SURFACE. 

Before  the  concrete  pavement  is  laid,  the  roadbed  shall  be  graded  Shaping 
to  a  true  cross-section,  conforming  to  the  grades  given  by  the  engineer  roadbed 
and  the  section  called  for  on  the  plans.  It  shall  then  be  watered  and 
rolled  with  a  roller  weighing  not  less  than  ten  (10)  tons  until  the  sur- 
face is  hard  and  unyielding.  The  width  to  be  rolled  shall  include  not 
less  than  one  foot  on  each  side  of  the  pavement  to  provide  satisfactory 
support  for  the  forms.  Depressions  shall  be  filled  with  fresh  material 
and  the  watering  and  rolling  continued  as  before.  Where  a  uniform 
and  unyielding  surface  cannot  be  otherwise  obtained,  the  surface  shall 
be  cultivated  and  again  rolled  until  a  uniform,  smooth  and  firm  foun- 
dation is  secured.  No  concrete  pavement  shall  be  laid  or  material 
deposited  upon  the  roadbed  until  it  is  in  a  condition  acceptable  to  the 
engineer. 

After  the  roadbed  has  been  prepared  as  hereinbefore  specified,  Forms 
forms  shall  be  constructed,  satisfactory  material  for  which  shall  be 
furnished  by  the  contractor.  The  proposed  concrete  pavement  is  to 
be  supported  on  each  side  by  two  inch  by  five  inch  (2"x5")  redwood 
lumber,  planed  straight  on  two  edges.  The  forms  are  to  be  set  true 
to  the  lines  and  grades  given  by  the  engineer  and  held  in  place  by 


138  GOOD  CONCRETE 

stakes,  of  such  size  and  length  and  set  at  such  intervals  as  may  be 
necessary  to  insure  rigidity.  The  stakes  shall  be  flush  at  the  top  with 
the  side  strips  and  the  entire  form  work  constructed  in  a  substantial 
and  workmanlike  manner.  The  forms  are  not  to  be  removed,  but 
are  to  remain  as  part  of  the  completed  work. 

Concrete       Cement:     All  cement  for  the  concrete  pavement  will  be  furnished 
pavement  by  the  County.     It  shall  be  Portland  Cement,  conforming  with  the 

Standard  Specifications  for  cement  adopted  in  August,  1 909,  by  the 

American  Society  for  Testing  Materials. 

The  cement  shall  be  suitably  protected  from  the  weather  and  piled 
so  as  to  permit  of  access  for  tally,  inspection  and  identification  of  each 
shipment.  It  will  be  delivered  in  the  original  package  with  the  brand 
and  the  name  of  the  manufacturer  plainly  marked  thereon.  The 
contractor  shall  be  held  responsible  for  the  proper  protection  and  safety 
of  the  cement  after  delivery  by  the  County.  He  shall  also  collect 
and  make  prepaid  return  shipment  of  empty  cement  sacks,  and  all 
shortage  of  cement  or  sacks  shall  be  charged  to  his  account. 

The  concrete  shall  be  composed  of  broken  stone  or  screened  gravel 
and  sand — all  of  which  shall  be  clean,  hard,  durable,  well  graded 
and  satisfactory  to  the  engineer — Portland  Cement  and  fresh,  clean 
water. 

Othet  The  sand  shall  be  of  such  size  that  all  of  it  will  pass  through  a 
materials  screen  having  four  (4)  meshes  per  linear  inch,  and  at  least  forty 
(40),  but  not  more  than  eighty-five  (85),  per  cent  by  weight  will 
be  retained  on  a  sieve  having  thirty  (30)  meshes  per  linear  inch. 
Not  more  than  seven  (7)  per  cent  weight  shall  pass  through  a  sieve 
having  one  hundred  ( 1 00)  meshes  per  linear  inch. 

The  broken  stone  or  gravel  stones  shall  vary  in  their  longest  dimen- 
sions from  one-half  ('/z)  of  an  inch  to  two  and  one-half  (2'/2) 
inches. 

Composition  Concrete  materials  shall  be  proportioned  as  follows:  One  (1 )  cubic 
foot  (95  pounds)  of  cement,  two  (2)  cubic  feet  of  sand,  and  four 
(4)  cubic  feet  of  broken  stone  or  screened  gravel,  and  water  which 


GOOD  CONCRETE 139 

shall  be  added  in  such  proportions  as  the  engineers  may  from  time 
to  time  determine. 

If  the  concrete  is  mixed  mechanically,  a  mixer  shall  be  used  which  Mixing  and 
is  satisfactory  to  the  engineer,  and  into  which  the  materials,  including  placing 
the  water,  can  be  precisely  and  regularly  proportioned. 

Hand-made  concrete  shall  be  mixed  on  a  tight,  level  platform,  as 
follows:  The  cement  and  sand  shall  first  be  thoroughly  mixed  dry 
in  the  proportions  specified.  Clean  water  shall  then  be  added  and 
the  materials  thoroughly  mixed  and  deposited  on  the  broken  stone  or 
screened  gravel,  which  has  been  previously  drenched  with  water.  The 
ingredients  shall  then  be  thoroughly  mingled  and  turned  over  until 
each  stone  is  covered  with  mortar.  The  batch  shall  be  carefully  de- 
posited without  delay  and  thoroughly  rammed  until  the  water  flushes 
to  the  surface  and  all  the  voids  are  filled.  Should  defective  work 
be  discovered  it  is  to  be  removed  and  the  space  refilled  with  fresh 
material  as  directed  by  the  engineer.  No  allowance  shall  be  made 
for  any  materials  or  labor  necessary  on  account  of  water. 

The  concrete  is  to  be  brought  to  a  true  and  uniform  surface  con- 
forming to  the  grade  and  cross  section  of  completed  roadway  as  shown 
on  drawings,  by  means  of  templates  and  such  other  implements  as 
may  be  necessary.  While  the  concrete  is  still  plastic,  it  is  to  be  finally 
finished  with  steel  floats  and  given  a  granolithic  surface,  which  shall 
be  free  from  any  unevenness. 

During  warm  and  dry  weather,  and  whenever  the  engineers  may 
direct,  all  newly-built  concrete  shall  be  kept  shaded  from  the  sun  and 
well  sprinkled  with  water. 

All  concrete  shall  be  measured  in  accordance  with  the  dimensions 
shown  on  the  plans  and  cross  sections. 

Concrete  pavement  will  be  paid  for  at  the  unit  price  per  square 
yard  for  concrete  pavement  in  place  complete,  which  price  shall  in- 
clude the  furnishing  of  all  materials,  all  labor,  tools,  implements,  forms 
and  all  work  on  same,  and  everything  incidental  and  necessary  to  the 
completed  work,  except  as  herein  otherwise  specified. 


140  GOOD  CONCRETE 

Bituminous        After  the  concrete  pavement  has  been  constructed  as  hereinbefore 
wearing  specified,  all  dust,  mud,  earth  or  foreign  material  of  any  kind  which 
surface   may  have   accumulated  upon  it  shall  be  removed  and  the  surface 
flushed  with  water.     When  it  has  become  sufficiently  hard  and  dry, 
and  in  the  opinion  of  the  engineer  is  ready  to  receive  it,  asphaltic 
oil  wil  be  furnished  and  applied  by  the  County.     It  will  be  put  in  one 
(1)  application  of  approximately  one-third  (1/3)  of  a  gallon  to  the 
square  yard.     All  the  work  hereinbefore  and  hereafter  provided  for 
shall  be  performed  by  the  contractor  except  the  application  of  as- 
phaltic oil. 

Directly  after  the  oil  has  been  applied,  stone  screenings  of  the 
commercial  size  known  as  Number  Four  (No.  4)  shall  be  uniformly 
spread  upon  it  in  sufficient  quantity  to  combine  with  the  oil  without 
leaving  any  excess  screenings  on  the  finished  road  surface.  The  stone 
screenings  are  to  be  spread  in  a  direction  parallel  with  the  road  and 
never  crosswise.  If  necessary,  from  time  to  time  additional  screen- 
ings shall  be  spread,  as  the  engineer  may  direct,  to  cover  any  oil 
which  may  come  to  the  surface,  until  the  final  completion  and  accept- 
ance of  the  work.  The  stone  screenings  are  to  be  furnished  and 
spread  by  the  contractor  and  must  be  of  a  quality,  size  and  spread 
in  a  manner  satisfactory  to  the  engineer. 

Protection  The  contractor  shall  exercise  due  precaution  to  prevent  damage 
of  pavement  to  the  work  during  the  various  stages  of  construction.  He  shall,  when- 
ever necessary,  construct  fences  or  barriers  to  prevent  travel  from 
passing  over  the  concrete  pavement  until  it  has  been  in  place  at  least 
seven  (7)  days,  or  over  the  oiled  surface  before  the  pavement  is 
completed.  Any  dust,  mud,  earth  or  foreign  material  carried  or  de- 
posited upon  the  concrete  pavement  which  is  to  be  oiled,  or  upon 
any  oiled  surface,  shall  be  removed  by  the  contractor  at  his  own 
proper  expense,  and  the  surface  thoroughly  cleaned  before  further 
work  progresses. 


GOOD  CONCRETE 


141 


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SPECIFICATIONS  FOR  STREET  PAVING 

WITH  ASPHALT  PAVEMENT 

IN  THE  CITY  OF  Los  ANGELES. 

(Specifications  No.  80.) 

Nolc — The  following  specificfiations  cover  the  materials  and  meth- 
ods of  preparation  for  sheet  asphalt  on  a  Portland  Cement  concrete 
base.  The  thickness  of  this  wearing  surface  for  very  heavy  traffic 
is  by  the  best  authorities  placed  at  2",  while  for  moderate  traffic  a 
thickness  of  \Yi"  will  be  ample. 

ASPHALT  WEARING  SURFACE. 

Upon  the  binder  course,  prepared  and  laid  as  above  described 
and  thoroughly  swept  free  from  all  rubbish,  shall  be  laid  an  asphalt 
wearing  surface  composed  of  asphaltic  cement,  sand  and  stone  dust, 
the  different  ingredients  being  mixed  in  such  proportions  that  the 
percentage  composition,  by  weight,  of  the  wearing  surface  shall  be 
within  the  following  limits: 

( I  )  Bitumen  soluble  in  carbon  disulphide — between  1 0  per 
cent  and  1 2  per  cent. 

(2)      Sand,  stone  dust  and  other  inorganic  ingredients,  as  follows: 

Passing  screen  of  200  mesh  to  the  inch,  between  1 0  per  cent 
and  1 4  per  cent. 


GOOD  CONCRETE 


Passing  screen  of  80  mesh  to  the  inch  and  rejected  by  screen  of  200 
mesh  to  the  inch,  between  20  per  cent  and  28  per  cent. 

Passing  screen  of  50  mesh  to  the  inch  and  rejected  by  screen  of 
80  mesh  to  the  inch,  between  20  per  cent  and  26  per  cent. 

Passing  screen  of  30  mesh  to  the  inch  and  rejected  by  screen  of 
50  mesh  to  the  inch,  between  1 8  per  cent  and  24  per  cent  . 

Passing  screen  of  20  mesh  to  the  inch  and  rejected  by  screen  of 
30  mesh  to  the  inch,  between  4  per  cent  and  8  per  cent. 

Passing  screen  of  10  mesh  to  the  inch  and  rejected  by  screen  of 
20  mesh  to  the  inch,  between  2  per  cent  and  5  per  cent . 

At  least  ten  (10)  per  cent,  and  not  more  than  eighteen  (18) 
per  cent  of  the  wearing  surface  shall  be  stone  dust. 

If  the  composition  contains  the  ingredients  aforesaid,  and  within 
the  percentages  above  fixed,  it  will  be  accepted  as  in  compliance 
with  this  paragraph. 

PAVEMENT  MATERIALS. 

Asphaltic  Cement:  The  asphaltic  cement  must  be  prepared  from 
California  products.  It  shall  be  a  mixture  of  a  refined  liquid  asphalt 
with  a  refined  solid  asphalt,  or  be  an  oil  asphalt,  and  must  be  free 
from  admixture  with  any  residues  obtained  by  the  artificial  distillation 
of  coal,  coal  tar,  or  parafhne  oil. 

The  asphaltic  cement  must  be  homogeneous  and  its  consistency 
at  the  time  of  its  use  must  fall  within  the  limits  of  sixty  (60)  degrees 
and  eighty  (80)  degrees  penetration  by  the  District  of  Columbia 
standard.  It  must  be  adhesive  and  ductile,  and  also  slightly  elastic 
at  a  temperature  of  thirty-two  (32)  degrees  Fahrenheit.  When 
twenty  (20)  gramme  are  heated  in  an  oven  to  a  temperature  of  three 
hundred  (300)  degrees  Fahrenheit  for  five  (5)  consecutive  hours 
in  an  uncovered  cylindrical  glass  dish  three  and  one-half  (3}/i)  cen- 
timeters high  by  five  and  one-half  (5^)  centimeters  in  diameter, 
it  must  not  lose  more  than  one  ( 1  )  per  cent  in  weight,  and  its  pene- 


GOOD  CONCRETE 


tration  must  not  be  reduced,  as  a  result  of  such  heating,  more  than 
fifty   (50)  per  cent. 

It  must,  when  ready  foi  use,  contain  at  least  ninety-nine  (99) 
per  cent  of  bitumen,  soluble  in  carbon  disulphide.  It  must  be  soluble 
in  carbon  tetra-chloride  to  the  extent  of  at  least  ninety-seven  and  one- 
half  (97J/2)  per  cent,  when  two  hundred  (200)  cubic  centimeters 
of  the  solvent  are  poured  on  one  gramme  of  the  asphaltic  cement  and 
the  mixture  is  allowed  to  stand  for  eighteen  (18)  hours  at  a  tempera- 
ture of  twenty-five  (25)  degrees  Centigrade  and  filtered  at  twenty- 
five  (25)  degrees  Centigrade.  Not  less  than  seventy  (70)  per  cent, 
shall  be  soluble  in  eighty-six  (86)  degree  naphtha  when  one  hundred 
and  fifty  ( 1  50)  cubic  centimeters  of  the  solvent  are  poured  on  one- 
half  O/i)  gramme  of  the  finely  divided  asphaltic  cement  and  the 
mixture  is  allowed  to  stand  for  eighteen  (18)  hours  at  a  temperature 
of  twenty-five  (25)  degrees  Centigrade  and  filtered  at  twenty-five 
(25)  degrees  Centigrade.  It  shall  not  contain  more  than  fifteen 
(15)  per  cent,  of  fixed  carbon  on  ignition. 

When  the  asphaltic  cement  is  prepared  by  mixing  a  solid  oil 
asphalt  with  a  liquid  asphalt,  the  solid  oil  asphalt  shall  be  prepared 
by  distilling  the  crude  oil  until  the  asphaltic  residuum  has  a  penetra- 
tion not  less  than  fifty  (50)  degrees  by  the  District  of  Columbia 
standard,  and  shall  not  be  prepared  by  mixing  or  fluxing  a  more 
solid  asphalt  with  liquid  or  softer  asphalt. 

The  refined  liquid  asphalt  used  in  softening  a  solid  asphalt  must 
be  a  stiff  residuum  of  petroleum  oil  with  an  asphalt  base.  It  must 
be  free  from  water  and  from  light  oils  volatile  at  less  than  two  hun- 
dred and  fifty  (250)  degrees  Fahrenheit.  When  twenty  (20) 
grammes  are  heated  in  an  oven  to  a  temperature  of  three  hundred 
(300)  degrees  Fahrenheit  for  five  (5)  consecutive  hours  in  an 
uncovered  cylindrical  glass  dish  three  and  one-half  (3  5/2)  centi- 
meters high  by  five  and  one-half  (5 Yl)  centimeters  in  diameter,  it 
must  not  lose  more  than  three  (3)  per  cent  in  weight.  It  must 
contain  not  less  than  ninety-nine  (99)  per  cent  of  bitumen  soluble  in 
carbon  disulphide. 


GOOD  CONCRETE  145 

The  sand  for  the  wearing  surface  shall  be  clean,  hard-  Sand 
grained  and  sharp,  and  shall  contain  not  more  than  three  (3)  per 
cent  of  loam,  clay  or  other  earthy  impurities;  it  must  all  pass  a  ten 
(10)  mesh  to  the  inch  screen,  and  not  less  than  seventy-five  (75) 
per  cent  of  its  volume  shall  pass  a  forty  (40)  mesh  to  the  inch 
screen. 

The   stone   dust   may   be   a   finely   powdered   limestone   or   other  Stone  dust 
hard    and    durable    rock    or    Portland    cement,    as    the    Contractor 
tractor  elects,  and  shall  be  of  such  fineness  that  all  of  it  will  pass  a 
fifty   (50)   mesh  to  the  inch  screen,  and  at  least  sixty-six  (66)  per 
cent  shall  pass  a  two  hundred  (200)  mesh  to  the  inch  screen. 

The  Contractor  shall  furnish  to  the  City  Engineer  by  test,  Samples 
whenever  called  for  and  free  of  charge,  samples  of  all  the 
materials  entering  into  the  composition  of  the  pavement,  the  asphalt 
and  asphaltic  cement  to  be  furnished  in  boxes,  and  said  City  Engineer 
shall  have  access  at  all  times  to  all  branches  of  the  work.  All  tests 
shall  be  open  to  the  Contractor. 

PREPARING  FOR  THE  WEARING  SURFACE. 

The  sand  shall  be  heated  in  suitable  driers  to  a  temperature  be- 
tween three  hundred  (300)  and  three  hundred  and  seventy-five 
(375)  degrees  Fahrenheit.  The  hot  sand  and  cold  stone  dust  shall 
then  be  thoroughly  mixed  together  in  a  suitable  mixer.  The  neces- 
sary quantity  of  asphaltic  cement  (previously  heated  to  between  two 
hundred  and  fifty  (250)  and  three  hundred  (300)  degrees  Fahren- 
heit) shall  then  be  added,  and  the  whole  mass  shall  be  mixed  until 
every  particle  of  the  sand  and  lime  dust  is  thoroughly  coated  with  a 
thin  layer  of  asphaltic  cement.  In  no  case,  after  refining,  shall  the 
asphaltic  cement  be  heated  above  three  hundred  and  twenty-five 
(325)  degrees  Fahrenheit. 

The  material  so  produced  must  leave  the  mixer  at  a  temperature 
between  two  hundred  and  fifty  (250)  and  three  hundred  and  twenty- 
five  (325)  degrees  Fahrenheit  and  must  be  fine-grained  and  capable 


M6 GOOD  CONCRETE 

of   producing    a    compact   pavement.      Proper    sand    and    sufficient 
asphaltic  cement  and  dust  must  be  used  in  order  to  secure  this  result. 

LAYING  THE  WEARING  SURFACE. 

The  surface  mixture,  prepared  as  above,  shall  be  brought  to  the 
work  in  suitable  carts  or  dump  wagons,  and  shall  not  be  colder  than 
two  hundred  and  fifty  (250)  degrees  Fahrenheit  or  hotter  than  three 
hundred  and  twenty-five  (325)  degrees  Fahrenheit  when  it  reaches 
the  street. 

It  shall  at  once  be  uniformly  spread  over  the  binder  course,  with 
hot  shovels  and  hot  rakes  to  such  a  depth  that,  after  receiving  its 
ultimate  compression,  the  finished  asphalt  wearing  surface  will  be  of 
a  thickness  not  less  than  that  shown  upon  the  cross-section  adopted 
for  the  work,  and  uniform  in  density  throughout  its  entire  thickness. 
Rakes  used  for  this  purpose  shall  have  strong  teeth  of  a  length 
sufficient  to  penetrate  through  the  entire  thickness  of  the  wearing 
surface. 

It  shall  be  immediately  compressed  by  a  roller  weighing  not  more 
than  one  hundred  and  twenty-five  (125)  pounds  to  the  lineal  inch 
width  of  tire,  after  which  a  small  amount  of  hydraulic  cement  or 
infusorial  earth  shall  be  swept  over  it,  and  it  will  then  immediately 
be  thoroughly  rolled  by  a  roller  weighing  not  less  than  210  pounds 
to  the  lineal  inch  width  of  tire.  This  rolling  must  be  continued  for 
not  less  than  five  (5)  hours  for  each  one  thousand  (1000)  square 
yards  of  pavement.  All  places  that  are  inaccessible  to  the  roller 
must  be  tamped  with  hot  iron  tampers.  The  resulting  pavement  must 
show  a  close-grained,  even  and  smooth  surface,  true  to  grade  and 
cross-section  and  free  from  al'  hollows  and  inequalities.  When  a 
straight  edge  five  (5)  feet  long  is  laid  on  the  finished  surface  of  the 
roadway  and  parallel  with  the  line  of  the  street,  the  surface  shall  in 
no  place  vary  more  than  one-quarter  (|/4)  of  an  inch  from  the  lower 
edge  of  the  straight  edge. 


GOOD  CONCRETE  147 

No  traffic  shall  be  allowed  on  the  street  until  the  pavement  is  thor- 
oughly cooled  and  set.  No  binder  or  wearing  surface  shall  be  laid 
in  rainy  weather  or  when  the  foundation  or  binder  is  wet  from  rain 
or  other  cause. 

All  cold  joints  shall  be  thoroughly  painted  with  hot  asphaltic 
cement. 

Where  stone,  brick  or  cement  gutters  are  not  provided  for,  the 
street  shall  be  paved  to  the  curb  and  the  surface  for  a  distance  of 
three  (3)  feet  next  to  the  curb  shall  be  coated  with  hot,  pure  asphalt 
and  smoothed  with  hot  smoothing  irons,  in  order  to  saturate  the 
pavement  to  a  certain  depth  with  an  excess  of  asphalt  and  make  the 
gutters  entirely  impervious  to  water. 


OTHER  TYPES  OF  WEARING  SURFACE. 
Sized  crushed  rock  bound  together  with  some  form  of  bitumen 
has  also  found  extensive  use  as  a  wearing  surface  placed  upon  a 
Portland  cement  base.  This  bituminous  concrete  is  usually  made 
from  1"  to  2-H"  in  thickness  and  is  technically  known  as  "Bitulithic" 
and  as  the  "Topeka  specification".  This  type  of  wearing  surface  is 
an  alternative  form  of  construction  to  an  asphalt  wearing  surface. 


CEMENT  PIPE 


CHAPTER  IX. 


CEMENT   PIPE. 

The  use  of  Portland  Cement  concrete  for  the  construction  of 
water  supply  and  drainage  projects  is  one  of  the  oldest  and  most 
extensive  applications  of  the  material. 

The  use  of  a  monolithic  construction  for  sewers  is  and  has  been 
for  a  long  time  considered  the  best  practice  even  by  those  who  are 
prejudiced  in  favor  of  brick  or  like  products  for  this  purpose.  Yet 
the  use  of  separately  moulded  cement  pipe  as  an  auxiliary  to  a 
monolithic  trunk  line  is  condemned  by  some  for  no  apparent  reason 
other  than  perhaps  that  it  is  a  serious  competitor  for  terra  cotta  pipe. 
Separately  moulded  concrete  pipe  possesses  advantages  over  glazed 
terra  cotta  that  are  apparent  to  even  the  most  casual  observer. 

A  cement  pipe  is,  first  of  all,  a  uniform  product  that  is  true  to  die.  Advantages 

A  concrete  pipe  moulded  in  any  given  section  preserves  that  sec-  °f 
tion  upon  hardening. 

It  does  not  warp,  and  two  consecutive  pieces  of  pipe  will  always 
fit  into  one  another  at  the  joints. 

It  can  be  made  upon  the  premises  by  local  labor  and  materials. 

It  eliminates  the  cost  of  hauling  a  factory-made  product  from 
some  distant  point  to  the  place  of  use. 


152 GOOD  CONCRETE 

Advantage       h  can  be  inspected  and  tested  while  being  made. 

It  is  stronger  than  a  terra  cotta  pipe  of  the  same  size. 
cement 

pipe       When  properly  made  it  is  more  impermeable  than  a  glazed  terra 
cotta  pipe. 

In  the  manufacture  of  terra  cotta  pipe  the  product  of  each  kiln 
must  be  segregated,  and  there  result  three  or  more  grades  of  pipe. 

In  the  manufacture  of  cement  pipe  the  entire  product  is  uniform. 

IRRIGATION  PIPE. 

The  agricultural  welfare  of  the  Southwest  depends  upon  the  eco- 
nomic conservation  and  distribution  of  water.  Water  is  wealth. 
The  seepage  from  open  flumes  and  the  loss  by  evaporation  is  a  direct 
financial  loss  to  the  irrigationist. 

Cement  irrigation  pipe  has  been  a  powerful  factor  in  the  develop- 
ment of  the  agricultural  resources  of  the  Pacific  Coast  States,  and 
the  means  of  efficiently  applying  water  in  irrigation  operations. 

CONTROLLING  FACTORS  IN  THE  MAKING  OF  GOOD  CEMENT 
PIPE  FOR  IRRIGATION. 

As  in  all  manufacturing  operations,  the  use  to  which  the  product 
is  to  be  put  will  control  the  quality  and  the  quantity  of  the  constituent 
materials.  The  large  majority  of  irrigation  pipe  for  tile  is  made  by 
hand.  The  equipment  is  very  simple  and  comparatively  inexpensive. 

Hand  made        Hand-made  tile  is  usually  of  the  tongue  and  groove  pattern.     One 
cement  pipe  end  of  the  pipe  is  formed  into  an  annular  groove,  the  other  into  a 
for   irrigation  tongue.     The  tongue  fits  into  the  groove  when  the  pipe  is  laid. 

Bell  ends  of  the  type  of  cast  iron  water  pipe  can  be  also  made 
by  hand,  but  are  not  as  convenient  to  handle  in  making  or  laying. 
The  ordinary  pipe  mould  consists  of  an  outer  shell  and  an  inner  core. 
The  outer  shell  is  so  constructed  that  it  can  be  expanded  by  a  simple 
lever  for  releasing  the  pipe.  The  core  is  so  made  that  it  can  be  col- 
lapsed by  simple  mechanical  means.  The  outer  shell  rests  on  a  pallet 


GOOD  CONCRETE  \53 

which  has  the  form  of  the  groove.  This  pallet  is  fastened  rigidly  on 
to  the  outer  shell.  The  top  of  the  outer  shell  is  fitted  with  a  funnel, 
and  the  core  is  topped  by  a  cone,  which  serves  to  guide  the  material 
into  the  mould.  The  material  is  tamped  into  the  moulds  with  iron 
tampers,  and  the  top  of  the  pipe  is  formed  into  the  "tongue"  by  press- 
ing and  rotating  a  suitable  ring  on  it. 

The  complete  mould  is  then  moved  to  the  storage  pile.  The  core  is 
collapsed  and  withdrawn  by  giving  it  a  twisting  motion  to  prevent 
tearing.  The  outer  shell  is  then  expanded  and  removed,  leaving  the 
pipe  resting  on  the  pallet.  The  pallet  is  not  removed  until  the  pipe 
has  become  strong  enough  to  handle. 

The  pallets  represent  the  greater  portion  of  the  equipment  neces- 
sary in  a  pipe  yard.  The  pipe-maker  will  need  a  supply  of  pallet 
rings  large  enough  to  handle  a  given  output.  The  pipe  can,  as  a 
rule,  be  lifted  from  the  pallets  at  the  end  of  two  or  three  days. 

MATERIAL  FOR  IRRIGATION  PIPE. 

Irrigation  pipe  up  to  the  size  of  24"  is  usually  made  of  sand 
and  cement  mortar.  The  corresponding  concrete  is  used  when  the 
thickness  of  the  shell  will  permit.  The  proportions  of  sand  to  cement 
vary  from  3:1  to  4 : 1  for  ordinary  tile. 

The  quality  of  the  pipe  depends  largely  upon  the  sand  used  in  its  Sand 
making.  The  pipe-maker  will  find  that  strict  attention  to  the  quality 
of  the  sand  will  net  him  a  direct  financial  return.  The  cement  pipe 
industry  has  grown  to  such  an  extent  within  the  past  few  years  that 
competition  is  now  very  keen  in  even  the  smallest  community,  which 
should  be  the  incentive  for  the  highest  quality. 

The  influence  of  the  sizing  of  grains  of  the  sand  upon  the  strength 
of  a  mortar  made  with  it  has  already  been  considered  at  length  on 
pages  30-32.  The  table  of  quantities  for  a  given  size  material  for 
the  "Concrete  Law"  should  be  closely  studied.  The  pipe-maker 
will,  for  certain  sizes,  find  it  a  positive  advantage  to  use  as  an  addi- 
tion to  his  sand  a  sized  one-half  inch  gravel  or  crushed  stone.  In 


154 


GOOD  CONCRETE 


the  following  table  the  effect  of  adding  sized  gravel  to  mortar  is  very 
strikingly  illustrated.  The  cement  and  sand  in  each  instance  were 
the  same. 


TABLE  XVII. 


No 

1 

^roportion 

i 

Proportion  of 

Compressive  Sir. 

Cement 

Sand 

Gravel 

to  Aggregate 

at  28  Days 

1 

2 

0 

:2 

21501bs. 

2 

2 

3 

:5 

2750  " 

3 

3 

0 

:3 

1383   " 

4 

3 

5 

:8 

1620   " 

5 

4 

0 

:4 

1060   " 

6 

5 

0 

:5 

532   " 

7 

6 

0 

:6 

165    " 

This  table  emphasizes  the  necessity  of  a  balance  between  the  sand 
and  rock  or  gravel.  For  example,  No.  2,  which  is  composed  of 
cement,  sand  and  gravel,  has  the  same  amount  of  cement  in  it  as  has 
No.  6,  which  is  composed  only  of  cement  and  sand.  Yet  No.  2  has 
a  strength  more  than  five  times  as  great  as  No.  6.  It  is  evident  that 
there  is  a  limit  to  the  amount  of  sand  that  can  be  used  in  a  mortar. 
As  the  proportion  of  sand  in  a  mortar  is  increased,  the  strength  de- 
creases very  rapidly. 

Quality  Different  sands,  and,  in  fact,  sands  from  the  same  locality,  show 
of  sands  a  wide  variation  in  their  percent  of  voids.  Referring  to  Table  IV, 
page  27,  it  will  be  seen  that  the  percent  of  voids  in  sands  is  by  no 
means  constant.  In  this  particular  instance  we  have  a  variation  from 
29%  to  40.5%.  The  tensile  and  compressive  strengths  of  the  1  :3 
mortar  is  greatest  for  sands  having  the  least  voids. 


GOOD  CONCRETE  155 

WEIGHT  PER  CUBIC  FOOT  As  AN  INDEX  TO  THE  PER  CENT  OF 
VOIDS. 

The  weight  per  cubic  foot  of  a  dry  sand  is  a  ready  means  for 
judging  its  percent  of  voids,  as  is  shown  in  Table  VI,  page  33. 
The  pipe-maker  should  aim  to  get  a  sand  whose  per  cent  of  voids 
is  as  low  as  possible,  and  whose  weight  per  cubic  foot  is  as  high 
as  possible.  By  the  exercise  of  a  little  thought  and  the  application 
of  the  principals  presented  in  this  book,  he  will  be  able  to  mix  two 
or  three  sands  in  such  a  manner  as  to  decrease  the  per  cent  of  voids 
and  increase  the  weight  per  cubic  foot  of  the  mixture,  thereby  in- 
creasing the  strength  and  density  of  his  product. 

The  mixing  of  mortar  is  usually  done  by  hand.  In  larger  yards  Mixing 
machine-mixing  is  resorted  to.  For  a  sand  and  cement  mortar  the 
only  machine  mixers  that  will  give  satisfactory  results  are  those  of 
the  trough  and  paddle  type,  in  which  the  material  is  fed  into  the 
horizontal  metal  trough  and  mixed  by  a  series  of  paddles  actuated 
from  a  central  shaft. 

AMOUNT  OF  WATER  AND  SIZE  OF  BATCH. 

The  amount  of  water  necessary  to  produce  a  mortar  of  the  proper 
consistency  is  a  most  important  item  in  cement  pipe  making.      In 
order  that  the  moulds  may  be  removed  as  soon  as  the  pipe  is  formed, 
the  mortar  must  of  necessity  be  of  a   "dry  consistency."      In  the   Consistency 
degree  of  "dryness"  lies  the  secret  of  making  an  impermeable  pipe,   of 
The  consistency  of  a  mortar  for  hand-made  pipe  is  usually  specified  mortar 
as  that  of   "damp  sand."     This  term  is,  however,  not  sufficiently 
specific.      It  will  be  more  definite  to  say  that  the  consistency  shall 
be  such  to  just  allow  the  moulds  to  be  removed  from  the  pipe  with- 
out adhering  to  it,  and  so  wet  that  the  pipe  will  just  stand  without 
sagging. 

In  order  to  properly  compact  the  sand  and  cement  mortar  there   Water  for 
must  be  present,  in  addition  to  the  water  necessary  for  proper  hard-  / 
ening,  an  amount  of  water  which  will  serve  as  a  lubricant  and  allow 


156  GOOD  CONCRETE 

the  sand  grains  to  become  coated  with  a  paste  of  cement,  and  to  slip 
on  one  another  into  the  most  compact  position. 

The  most  common  error  committed  by  pipe-makers  is  to  use  too 
dry  a  mortar.  It  is  only  by  using  the  right  amount  that  the  full 
strength  of  the  pipe  can  be  developed. 

Evaporation         The  proper  degree  of  water  must  be  maintained,  and  to  this  end 

from    *ne  size  °f  a  batch  should  be  such  that  the  water  will  not  evaporate 

mortar    before  the  mortar  is  moulded  into  the  pipe.     In  Summer  it  will  take 

but  a  very  few  moments  to  evaporate  from  1 0  to  \2%  of  the  water 

in  a  mortar.      Care   should   therefore   be   exercised   to   prevent   this 

evaporation   by  providing  suitable  working  sheds   under   which   the 

work  is  done. 

CURING  THE  PIPE. 

The  green  pipe  should  be  protected  from  strong  drafts  and  direct 
sunlight.  Water  is  constantly  applied  in  a  fine  spray  to  the  pipes  as 
soon  as  they  are  a  few  hours  old.  The  pipe  should  be  cured  for  at 
least  three  weeks  before  placing  in  the  ground. 

LAYING. 

The  properly  cured  pipe  are  laid  in  a  trench  excavated  to  grade. 
Each  joint  is  carefully  cleaned  and  soaked  with  clean  water.  A 
mortar  consisting  of  1  part  sand  and  1  part  cement  of  the  con- 
sistency of  putty  is  then  applied  to  the  tongue  and  groove  and  the 
pipe  brought  together.  The  exterior  is  then  covered  with  this  same 
mortar,  to  cover  the  joint,  and  finished  by  wiping  with  the  gloved 
hand. 

The  inside  of  the  joint  must  also  be  "wiped"  smooth. 

GENERALLY. 

The  bedding  of  the  pipe  in  the  trench  is  a  very  important  opera- 
tion and  one  to  which  too  little  attention  is  usually  paid. 

If  the  pipe  is  not  carefully  bedded  by  properly  back  filling  around 


GOOD  CONCRETE 157 

the  entire  lower  half  the  earth  will  arch  and  leave  a  portion  of  pipe 
unsupported.  Any  settlement  that  takes  place  will  then  crack  the 
pipe.  Proper  bedding  is  important  even  in  cast  iron  pipe. 

The  pipe  line  should  be  supplied  with  air  vent  valves  at  all  points 
where  there  is  a  change  in  the  grade. 

All  valves  for  controlling  the  flow  of  the  water  should  be  of  such 
design  that  in  closing  they  do  not  produce  a  water  hammer. 

Stand  pipes  with  proper  valves  should  be  provided  at  proper 
intervals  as  a  relief  for  any  pressure  in  excess  of  the  safe  working 
strength  of  the  pipe. 

Hand-made  pipe  may  for  lines  carrying  a  high  pressure  be  rein- 
forced with  hoops  of  wire,  which  are  dropped  into  the  moulds  while 
forming  the  pipe  and  spaced  about  1 J/2  inches  apart. 

Reinforced  concrete  pipe  should  only  be  made  in  accord  with 
plans  furnished  by  a  competent  engineer. 


UNITS  OF  MEASUREMENT  USED  IN  MEASURING 

WATER. 

The    Federal   Government   uses   the   cubic   foot  per   second   for   Cubic  feet 
measuring  all  water.      Engineers  generally  use  the  same  unit.      A   Pejr 
cubic  foot  per  second,  or  "second  foot,"  is  the  amount  of  water  that   second 
will  flow  past  a  point  in  a  channel  having  a  sectional  area  of   1 
square  foot  with  a  velocity  of  1  foot  per  second. 

In  California  there  is  a  local  unit  used  termed  the  "Miner's  inch."    '  "e  m*ner  5 
A  miner's  inch  has  two  values.     The  old,  and  most  generally  used,    mc" 
value  is  equivalent  to    1/50  of  a  cu.    ft.  per  second.      The  new 
value,   which  was  defined  by  the  California  Legislature  of    1 90 1 , 
places  the  equivalent  of  a  miner's  inch  at  1/40  cu.  ft.  per  second. 
The  old  value  is,  however,  most  generally  used,  and  in  contracts  for 
a  water  supply,  unless  otherwise  specified,   the  old  miner's  inch  is 
the  accepted  unit. 

VALUES  OF  ONE  CUBIC  FOOT  PER  SECOND. 

1  cu.  ft.  per  second  =  50  Old  Miners'  inches  =  8.97  gals,  per  min. 
1  cu.  ft.  per  second  =•  40  New  Miners'  inches  =  1  1 .22  gals,  per  min. 
1  cu.  ft.  per  second  =  448.8  gals,  per  min.  =  646.272  gals,  per  day 

(24  hours) 
1   cu.  ft.  per  second  is  approximately  one  acre  covered  one  inch  in 

depth  per  hour. 
1  cu.  ft.  per  second  is  one  acre  covered  1 .98  feet  deep  in  24  hours. 


160 


GOOD  CONCRETE 


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GOOD  CONCRETE 


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162 


GOOD  CONCRETE 


1  cu.  ft.  of  water  weighs  62.5  pounds. 

1  cu.  ft.  of  water  contains  7.48  gallons. 

I  Acre  Foot  is  one  acre  covered  with   1    foot  of  water. 

1  Acre  Foot=43,560  cu.  ft. 

To  use  To  Use  Table:  Let  it  be  required  to  find  the  size  of  pipe  neces- 
table  sary  to  carry  30  miner's  inches  (old)  of  water  when  the  pipe  line 
is  2,500  feet  long  and  having  a  total  fall  of  10  feet.  First  reduce 
the  total  fall  to  feet  fall  per  1 ,000  feet.  Thus  10  feet  fall  in  2,500 
feet  of  line  is  equivalent  to  4  feet  per  1 ,000.  In  the  first  column 
of  table  find  "4  feet,"  and  on  the  same  horizontal  line  opposite  find 
the  number  under  "Miner's  inches"  which  is  next  larger  than  30. 
This  is  found  to  be  34.15,  and  this  corresponds  to  an  8"  pipe. 

PLAIN  CONCRETE  PIPE  TABLE 


Size 

w< 

pa 

h. 

Ti.ickr.,  « 
of 

Contents  in 
cu.  ft.  prr 

Lin.  ft.  Pipe 
per  cu.  yard 

Lin.  ft. 
perbbl. 

Lin.  ft. 
perbbl. 

Lin.  ft. 
perbbl. 

Wet 

Dry 

Shell 

Linear  ft. 

Sand&Grav. 

1:3  Mix 

1:4  Miz 

6" 

23# 

20# 

IV 

,16 

138 

75 

87 

100 

8" 

10" 

36 
53 

31 

44 

!%- 

.25 
.35 

88 

62 

48 
34 

56 

40 

s 

12" 

70 

57 

IK" 

.45 

48 

26 

31 

35 

14" 

88 

68 

}%' 

.56 

38 

21 

24 

28 

16" 

103 

90 

]%'" 

.68 

32 

17 

20 

24 

18" 

130 

100 

\%" 

.82 

26 

14 

17 

•     19 

20" 

136 

114 

\%  " 

.90 

24 

13 

15 

17 

22" 

176 

141 

2     " 

.05 

20 

11 

13 

15 

24" 

220 

163 

2X" 

.30 

18 

9 

10 

12 

26" 

225 

180 

2X  " 

.40 

16 

8 

10 

11 

28" 
30" 

265 
286 

208 
225 

2H" 

.66 
.80 

14 
12 

7 
6 

7 

9 
8 

32" 

333 

260 

3     " 

2.08 

10 

5 

6 

7 

36" 

408 

320 

3     " 

3.55 

8 

4.7 

5 

6 

GOOD  CONCRETE 


WEIR  TABLE 
Giving  Cubic  Feet  of  Water  per  Minute  that  will  flow  over  a  weir  one 

inch  wide  and  from  1A  to  20%  in.  deep. 
For  other  widths  multiply  by  the  width  in  inches. 


In. 

Cu.  ft. 

#in. 
Cu.ft. 

#in. 

Cu.ft. 

H  in. 
Cu.ft. 

Kin. 
Cu.ft 

Kin. 
Cu.ft. 

X'm. 
Cu.ft. 

* 

%  in. 
Cu.fl. 

0 

.00 

.01 

.05 

.09 

.14 

.19 

.26 

.32 

1 

.40 

.47 

.55 

.64 

.73 

.82 

.92 

1.02 

2 

1.13 

1.23 

1.35 

1.46 

1.58 

1.70 

1.82 

1.95 

3 

2.07 

2.21 

2.34 

2.48 

2.61 

2.76 

2.90 

3.05 

4 

3.20 

3.35 

3.50 

3.66 

3.81 

3.97 

4.14 

4.30 

5 

4.47 

4.64 

4.81 

4.98 

5.15 

5.33 

5.51 

5.69 

6 

5.87 

6.06 

6.25 

6.44 

6.62 

6.82 

7.01 

7.21 

7 

7.40 

7.60 

7.80 

8.01 

8.21 

8.42 

8.63 

8.83 

8 

9.05 

9.26 

9.47 

9.69 

9.91 

10.13 

10.35 

10.57 

9 

10.80 

11.02 

11.25 

11.48 

11.71 

11.94 

12.17 

12.41 

10 

12.64 

12.88 

13.12 

13.36 

13.60 

13.85 

14.09 

14.34 

11 

14.59 

14.84 

15.09 

15.34 

15.59 

15.85 

16.11 

16.36 

12 

16.62 

16.88 

17.15 

17.41 

17.67 

17.94 

18.21 

18.47 

13 

18.74 

19.01 

19.29 

19.56 

19.84 

20.11 

20.39 

20.67 

14 
15 

20.95 
23.23 

21.23 
23.52 

21.51 
23.82 

21.80 
24.11 

22.08 
24.40 

22.37 
24.70 

22.65 
25.00 

22.94 
25.30 

16 

25.60 

25.90 

26.20 

26.50 

26.80 

27.11 

27.42 

27.72 

17 

28.03 

28.34 

28.65 

28.97 

29.28 

29.59 

29.91 

30.22 

18 

30.54 

30.86 

31.18 

31.50 

31.82 

32.15 

32.47 

32.80 

19 

33.12 

33.45 

33.78 

34.11 

34.44 

34.77 

35.10 

35.44 

20 

35.77 

36.11 

36.45 

36.78 

37.12 

37.46 

37.80 

38.15 

CHAPTER  X. 


CEMENT  SEWER  PIPE. 

The  attributes  of  Portland  Cement  concrete  which  have  found 
for  it  such  a  widespread  use  as  a  material  for  the  construction  of 
monolithic  sewers  would  most  naturally  recommend  it  for  sewer  pipe 
of  smaller  cross-section. 

The  economies  to  be  affected  by  the  use  of  separately  moulded 
concrete  pipe  are  such  as  would  certainly  entitle  it  to  consideration 
in  competition  with  pipe  of  other  materials. 

That  there  have  been  a  great  many  wretched  cement  pipes  made 
in  the  past  cannot  be  denied,  nor  can  the  same  be  denied  for  terra 
cotta  pipe.  In  the  early  days  of  the  cement  pipe  industry,  Portland 
Cement  was  both  expensive  and  uncertain  in  quality,  and  the  condi- 
tions were  not  so  favorable  for  good  concrete  as  they  are  today.  To 
sweepingly  condemn  cement  pipe  on  the  failures  of  the  first  attempts 
without  analyzing  the  causes  of  these  failures  is  not  only  unjust  but 
unintelligent. 

WHAT  Is  NEEDED  FOR  GOOD  CEMENT  SEWER  PIPE. 

The  principles  of  cement  pipe  construction  for  irrigation  hold 
also  for  sewer  pipe.  A  sewer  pipe  will  be  subjected  to  different 
service  conditions  than  will  an  irrigation  pipe.  Its  constituent  ma- 
terials should  therefore  be  so  selected  as  to  meet  the  requirements 


166  GOOD  CONCRETE 

of  these  conditions.     A  sewer  pipe  must,  first  of  all,  be  impermeable, 
Necessary    and  the  relatively  greater  depths  at  which  it  is  usually  imbedded 
strength    under  the  ground  surface  will  necessitate  a  somewhat  stronger  mix- 
ture than  is  customarily  used  for  making  irrigation  pipe. 

Cause  of  Thfi  most  common  cause  of  collapse  of  both  terra  cotta  and  cement 
collapse  sewer  pipe  is  the  lack  of  care  used  in  bedding  the  pipe  in  the  sewer 
trench.  With  careless  back-filling  and  tamping,  the  earth  arches  and 
leaves  a  portion  of  the  lower  segment  of  the  pipe  unsupported, 
which,  when  the  depth  of  fill  is  sufficient,  will  cause  the  pipe  to 
crack. 

Impermeability        Impermeability  can  only  be  obtained  by  using  a  comparatively 

depends  upon   wet  mortar  or  concrete.     The  pipe  may  also  be  given  a  wash  on 

the   consistency   the  interior  with  neat  cement  cream.     Impermeability,  however,  to 

of  the  mixture   be  of  a  lasting  value,  must  be  obtained  in  the  making  of  the  pipe 

rather  than   in   subsequent  treatment.      Impermeability  will   depend 

upon  the  degree  to  which  the  voids  in  the  sand  or  the  aggregate  are 

filled  with  cement  paste,  and  upon  the  use  of  the  proper  amount  of 

water  in  mixing. 

CEMENT  SEWER  PIPE  IN  EUROPE. 

The  manufacture  of  separately  moulded  cement  sewer  pipe  has 
in  Europe  become  a  highly  organized  industry.  The  European 
manufacturer  of  this  class  of  pipe  does  not  confine  himself  to  circular 
sections,  as  does  the  American.  For  the  larger  sizes  of  pipe  the 
section  is  sometimes  egg-shaped,  with  a  flat  base  to  allow  the  proper 
bedding.  The  ease  and  perfection  with  which  the  European  cement 
pipe-maker  produces  Y's,  T's,  elbows  and  siphons  of  large  and 
small  diameter  would  indicate  that  the  sewer  pipe  industry  in  Europe 
has  reached  the  dignity  of  an  art. 

The  extent  to  which  cement  or  concrete  pipe  is  used  in  Germany 
may  be  realized  when  we  consider  the  words  of  a  very  prominent 
German  sanitary  engineer,  who  in  a  recent  lecture  made  a  remark 
that  brick  as  a  material  for  constructing  sanitary  sewers  was  only 
of  historic  interest! 


PLATE  XXX. 


SEPARATELY  MOULDED  CONCRETE  SEWER  PIPE, 
KOENIGSBERG,  PRUSSIA. 


GOOD  CONCRETE 


167 


Perhaps  the  largest  sewer  in  existence  built  of  separately  moulded 
concrete  pipe  is  that  in  Koenigsberg,  in  Prussia.  The  pipe  here  are 
7  feet  3  inches  in  internal  diameter  with  a  shell  thickness  of  6". 

MACHINE-MADE  CEMENT  PIPE. 

Within  the  past  few  years  cement  sewer  pipe  has  been  very  suc- 
cessfully made  by  machine.  The  machine-made  product  possesses 
marked  advantages  over  the  hand-made.  The  so-called  glazed 
cement  pipe  machine  produces  a  product  whose  density  and  imper- 
meability leave  nothing  to  be  desired.  The  principle  of  this  machine 
is  a  revolving  core,  which  not  only  serves  to  compact  the  mortar,  but 
to  give  the  interior  of  the  pipe  a  polished  troweled  surface.  It  was 
the  product  of  this  machine  which  recently  in  San  Diego  vindicated 
the  cause  of  cement  sewer  pipe.  The  adoption  by  the  municipal 
authorities  of  San  Diego  of  cement  sewer  pipe  was  so  bitterly  resented 
by  the  competitors  in  terra  cotta  that  in  self-justification  the  city 
engineer  had  to  resort  to  the  unprecedented  procedure  of  testing,  every 
single  piece  of  pipe  for  a  length  of  several  miles. 

RESULTS  OF  A  PUBLIC  TEST  MADE  AT  THE  SAN  DIEGO  INDUS- 
TRIAL FAIR,  FEBRUARY  24,  1913. 


8" 

Vitrified  Cla\)  Pipe. 

8"  Glazed  Cement  Pipe. 

No.   1. 

With    15    Ibs.   pressure, 

No.   2.  Subjected    to     15     Ibs. 

commenced  to  seep  in  3 

pressure    for   5    minutes 

minutes  and  broke  at  55 

and    broke    at    80    Ibs. 

Ibs.   pressure. 

pressure,  with  no  seepage 

N.  3. 

Small  seepage  in  5  min- 
utes under  1  5  Ibs.  pres- 

whatever. 
No.  4.   Subjected    to     15    Ibs. 

sure.     Broke  at  65  Ibs. 

pressure    for   4   minutes 

pressure. 

and  broke  at    1  1  5   Ibs. 

No.  5. 

Under  15  Ibs.  pressure, 
showed    seepage    in     1 
minute  and  broke  at  73 

pressure,   with  no  seep- 
age whatever. 
No.   6.   Pressure  was  held  at  1  5 

Ibs.  pressure. 

Ibs.  for  3  minutes,  then 
slowly   run   up  to    125 

Ibs.,  then  in  jumping,  the 

pressure  to  150  Ibs.  the 

pipe  broke.    No  seepage 

whatever. 

168 GOOD  CONCRETE 

The  results  of  these  tests  have  been  given  wide  publicity  and  have 
served  to  not  only  justify  the  Municipal  authorities,  but  to  effectually 
silence  the  "influences"  through  whose  efforts  these  tests  had  to  be 
undertaken. 

The  pipe  used  in  the  above  tests  was  selected  from  "stock"  and 
each  manufacturer  knew  that  the  specimens  were  to  be  used  for  a 
public  test. 

The  favor  with  which  machine-made  cement  sewer  pipe  is  regarded 
by  the  foremost  in  the  engineering  profession  will  be  realized  by  quot- 
ing the  testimony  given  before  the  San  Diego  City  Council  in  the 
sewer  controversy.  The  late  James  Dix  Schuyler  as  a  witness  was 
examined  by  Councilman  Adams. 

Q.  (by  Mr.  Adams)  :  Mr.  Schuyler,  what  do  you  think  of  the 
pipe  you  saw  being  made  for  the  City  of  San  Diego? 

A.  (by  Mr.  Schuyler)  :  I  think  so  well  of  it  that  I  would  use  it 
in  preference  to  any  vitrified  clay  pipe. 

Q.  (by  Mr.  Adams)  :  Mr.  Schuyler,  that  is  a  strong  statement 
and  you  are  a  man  of  international  reputation.  Do  you  realize  that 
your  statements  are  being  recorded  and  will  become  public?  Would 
you  be  willing  to  stake  your  reputation  on  the  use  of  cement  pipe 
for  sanitary  sewers? 

A.  (by  Mr.  Schuyler)  :  If  I  could  get  such  machine-made  pipe 
as  I  have  seen  here,  I  would.  In  hand-made  pipe  there  is  likely  to 
be  more  variation,  but  this  pipe  is  remarkably  uniform. 

Q.  (by  Mr.  Adams)  :  What  is  your  opinion  of  the  effect  of 
sewer  gases  on  cement  pipe? 

A.  (by  Mr.  Schuyler)  :  I  have  not  had  much  actual  experience, 
but  have  read  considerably  about  it.  My  opinion  is  that  the  gases 
in  sewers  cannot  affect  a  dense  cement  pipe  such  as  this  is. 

Q.  (by  Mr.  Adams)  :  You  say  that  you  would  prefer  this  pipe 
to  vitrified  clay  pipe? 

A.   (by  Mr.  Schuyler)  :     Yes,  sir. 


GOOD  CONCRETE 


Q.  (by  Mr.  Adams)  :  If  you  were  City  Engineer  of  San  Diego, 
would  you  use  this  glazed  cement  pipe  for  the  city  sewers  and  recom- 
mend its  use  to  this  City  Council? 

A.  (by  Mr.  Schuyler)  :  Yes,  sir ;  I  would  do  so  without  any 
hesitation. 

Mr.  Schuyler  was  then  examined  by  Attorney  H.  J.  Stevens. 

Q.  You  have  had  a  great  deal  of  experience  with  cement,  have 
you  not? 

A.      Yes,  sir;  for  many  years. 

Q.      I   believe  you  built  the  Sweetwater  Dam? 

A.      Yes,  sir. 

Q.  Have  you  ever  made  any  tests  yourself  in  order  to  bring 
out  the  qualities  of  vitrified  clay  pipe  as  compared  with  cement  pipe? 

A.  I  have  made  tests,  and  very  recently.  Specimens  of  vitri- 
fied clay  pipe  were  procured  from  an  inspector  of  the  street  de- 
partment of  Los  Angeles.  My  representative  went  to  a  point  where 
a  sewer  was  under  construction  and  procured  pipe  which  had  been 
accepted  as  passing  the  Los  Angeles  city  specifications,  and  which 
were  lying  by  the  side  of  the  trench  ready  to  be  laid  in  place.  Care 
was  taken  to  choose  the  specimens  having  a  particularly  fine  glaze. 
I  have  been  told  they  were  "top"  joints,  meaning  that  they  were 
burned  in  the  top  tier  of  the  sewer  pipe  kiln,  and,  as  a  consequence, 
received  the  most  intense  heat  and  the  heaviest  salt  glaze.  When 
this  pipe  was  submitted  to  the  test  to  determine  permeability — that  is, 
filld  with  water  under  pressure — I  was  astonished  to  see  the  water 
percolate  freely  through  the  shell  of  the  pipe  at  from  5  to  10  Ibs. 
pressure.  At  1 5  Ibs.  it  shot  out  in  every  direction  in  innumerable 
fine  streams.  If  you  gentlemen  had  seen  this  test,  your  confidence 
in  clay  pipe  would  have  been  shaken  as  mine  was.  The  results  were 
shocking,  yet  I  can  vouch  for  the  absolute  fairness  of  the  test,  except- 
ing that  the  specimens  were  considerably  above  the  average  in  quality. 


170  GOOD  CONCRETE 

One  or  two  sections  of  merely  average  pipe  which  had  been  ac- 
cepted by  the  City  of  Los  Angeles  were  submitted  to  the  test  described 
above.  In  one  case  it  was  impossible  to  move  the  needle  on  the 
pressure  gauge,  as  the  water  flowed  through  the  porous  shell  of  the 
pipe  so  freely  that  no  pressure  could  be  procured." 

The  various  manufacturers  of  machine-made  cement  sewer  pipe 
will,  to  our  definite  knowledge,  guarantee  their  product  to  be  as  im- 
permeable and  as  strong  as  the  best  vitrified  clay  pipe,  and  they  will 
welcome  the  opportunity  of  having  their  product  publicly  tested 
against  vitrified  clay  pipe  of  the  same  size. 


CHAPTER  XI. 


SOME  SUGGESTIONS  FOR  THE  CARE  AND  RETURN 
OF  EMPTY  SACKS. 

Like  any  other  commodity,  cement  makes  its  special  requirement 
of  everyone  concerned  in  handling  it,  whether  it  be  the  consumer,  the 
dealer  or  the  manufacturer.  We  can  appropriately  conclude  this  book 
on  the  correct  usage  of  Portland  Cement  with  some  remarks  upon  its 
peculiarities  as  an  article  of  commerce. 

CARE  OF  SACKS. 

The  sacks  in  which  cement  is  shipped  are  perishable  property  of  a    Sacks 
highly  valuable  nature,  employed  because  of  necessity  by  the  manu-    are 
facturer  of  cement  to  convey  his  product  to  the  consumer  of  cement. 
Disregard   of   the   business  principles   underlying  the   transaction   is 
sure  to  result  in  loss  and  discontent  to  him  who  neglects  them.     The 
best  statement  of  these  principles  that  we  have  ever  seen  was  made 
by  Mr.  L.  T.  Sunderland,  Vice-President  of  the  Ash  Grove  Lime 
&  Portland  Cement  Co.,  before  a  meeting  of  the   Retail  Lumber 
Dealers  of  Kansas  on  September  15,  1912.     We  reprint  his  paper, 
entitled: — 

SACK  LOSSES 
WHO  SHOULD  BEAR  THEM? 

"Many  cement  users  contend  that  worn-out  and  unserviceable  cloth 
sacks  should  be  redeemed,  and  the  loss  incident  to  wear  and  tear,  losses 


172 GOOD  CONCRETE 

abuse  and  misuse  while  in  service,  should  be  borne  by  the  manufac- 
turer whose  brands  such  sacks  carry. 

"Such  a  contention  is  often  based  on  the  erroneous  assumption  that 
manufacturers — 

(a)  Use  cloth  sacks  for  their  own  convenience. 

(b)  Make  a  large  profit  on  them;  and 

(c)  Merely  loan  them  to  the  purchasers  of  cement 

to  be  returned  when  empty. 

"As  not  one  of  these  assumptions  is  correct,  such  a  conclusion  must 
fall. 

"The  facts  are: 

Why  a        "First.      Manufacturers  use  cloth  sacks  from  sheer  necessity,  there 
cloth  sack?    being  no  other  package  that  can  be  substituted  without  imposing  in- 
creased burdens  upon  the  dealer  in,  or  user  of,  cement.     There  are 
two  other  kinds  of  packages  that  have  been  used  to  a  limited  extent, 
viz:     Wooden  barrels  and  paper  bags. 

Barrels  "Wooden  barrels  are  out  of  the  question  because  of  increased  cost 
of  packing  the  cement  into  them;  the  large  initial  cost  of  the  barrel 
itself  (35  to  40  cents  each)  ;  the  inconvenience  in  handling  a  pack- 
age weighing  400  pounds,  especially  on  large  work;  the  increased 
cost  represented  by  freight  on  weight  of  each  barrel  (approximately 
25  pounds)  ;  and  the  increased  cost  of  the  cement  to  the  dealer  and 
user  because  the  barrel  cannot  be  returned.  It  will  be  seen,  there- 
fore, that  the  use  of  the  wooden  barrel  would  entail  a  direct  addi- 
tional tax  on  the  dealer  or  user — all  items  considered — of  approxi- 
mately 40  cents  per  barrel.  There  were  78,000,000  barrels  of 
cement  produced  in  the  United  States  in  1911,  and  if  all  had  been 
packed  or  shipped  in  wooden  barrels  the  additional  cost  of  that  cement 
to  the  ultimate  consumer  would  have  been  $31,200,000  on  that  one 
year's  production. 

Paper  bags        "Paper  bags  are  used  to  a  very  limited  extent.     They  cost  the 
manufacturer   10  cents  per  barrel   (four  bags  to  a  barrel),  and  the 


GOOD  CONCRETE 173 

additional  burden  to  the  dealer  and  user  is  represented  by  this  10 
cents  per  barrel,  plus  the  loss  resulting  from  breakage  in  transporta- 
tion and  handling,  which  is  large  (probably  5  cents  per  barrel)  and 
very  annoying.  The  shippers  will  not  be  responsible  for  damage 
to  paper  bags,  which  at  best  are  too  weak  for  the  load  they  carry, 
and,  on  the  whole,  paper  bags,  which  cannot  be  saved  or  returned, 
impose  an  additional  and  wholly  unnecessary  burden  of  approximately 
1  5  cents  per  barrel — all  items  considered — on  the  ultimate  consumer, 
which,  when  applied  to  the  78,000,000  barrels  of  cement  produced 
in  191 1,  would  represent  $1 1,700,000  for  one  year. 

"The  cloth  sack  is  the  only  practical  package  available.  It  will 
stand  transportation,  its  size  and  shape  make  it  convenient  to  handle, 
and  it  is  returnable  at  the  option  of  the  dealer.  If  properly  cared 
for  it  may  be  used  over  and  over  again  many  times. 

"The  use  of  the  cloth  sack  (which,  as  shown  below,  places  a  bur- 
den on  the  ultimate  consumer  of  only  5  cents  per  barrel),  when 
proper/];  handled,  is  a  source  of  little,  if  any,  loss  to  the  dealer  save 
the  cost  of  bundling  and  prepaying  freight  to  the  mill.  (A  dealer 
should  not  accept  from  his  customer  any  but  serviceable  sacks — all 
serviceable  sacks  are  accepted  by  the  manufacturer;  therefore  if  the 
dealer  sustains  losses  of  any  consequence  it  is  his  own  fault.) 

"Second.  Manufacturers  do  not  make  a  profit  on  the  cloth  sacks; 
on  the  contrary,  they  usually  sustain  serious  losses.  The  price  of 
standard  cloth  cement  sacks  today  is  approximately  $100  per  thou- 
sand (10  cents  each)  in  carload  lots,  and  the  cost  of  the  material 
from  which  they  are  made  is  increasing.  The  best  cement  manufac- 
turers have  facilities  for  cleaning  and  repairing  sacks,  and  give  deal- 
ers full  credit  for  all  sacks  that  may  be  readily  repaired.  This  is  a 
large  expense,  borne  altogether  by  the  manufacturer;  hence  it  will 
be  seen  the  manufacturer  sustains  an  actual  loss,  which  at  times  is 
quite  serious. 

"Third.  When  a  miller  ships  flour  he  sells  the  package  (sack  or 
barrel)  with  the  flour,  but  the  packages  are  not  returnable.  Like- 


1J74 GOOD  CONCRETE 

wise  with  lime — the  barrel  (or  sack,  if  hydrated  lime)  is  included  in 
the  price.  With  cement,  as  with  flour  and  lime,  the  price  includes  the 
packages  which  are  sold  with  the  cement.  The  sacks  are  not  loaned, 
but  are  sold  outright.  The  dealer  is  under  no  obligation  to  return 
them,  but  the  manufacturer  extends  the  dealer  the  privilege  of  so 
doing  if  he  chooses,  at  a  certain  price  under  certain  conditions. 

"Cloth  sacks  wear  out  largely  while  in  consumer's  hands,  therefore 
the  consumer  should  bear  the  loss  incident  thereto. 

"If  a  cloth  cement  sack  can  be  used  eight  times,  as  it  may  be  if 
properly  cared  for  and  returned  promptly  when  empty,  the  loss  or 
burden  imposed  upon  the  ultimate  consumer  from  the  use  of  cloth 
sacks  is  only  five  cents  per  barrel,  which  is  only  one-third  the  burden 
imposed  by  the  use  of  paper  bags,  and  one-eighth  the  burden  im- 
posed by  the  use  of  wooden  barrels. 

"Cheaper  cloth  sacks  than  those  now  used  for  carrying  cement  are 
out  of  the  question,  because  they  are  too  frail  and  weak  to  stand 
transportation  and  protect  the  heavy  weight  of  cement." 

RETURN  OF  EMPTY  SACKS. 

Empty  sacks       Western  Classification  Exception  Sheet  provides  that   all  empty 

must  be  sacks  must  be  prepaid  before  acceptance  by  carriers,  and  this  rule 

Prepaid  will  be  rigidly  enforced  in  future.     The  Southern  Pacific,  Santa  Fe, 

S.  P.,  L.  A.  &  S.  L.,  and  Pacific  Electric  Railway  Companies  have 

all  taken  a  firm  stand  in  this  regard,  and  we  call  your  attention  to  the 

rule  to  avoid  misunderstanding  and  consequent  delay. 

The  Riverside  Portland  Cement  Company  prints  a  set  of  rules 
for  the  guidance  of  its  customers  when  returning  empty  sacks,  a 
copy  of  which  is  furnished  with  every  car  of  cement.  The  instruc- 
tions given  on  the  placard  are  quoted  below,  and  the  illustrations 
reproduced. 


How  TO  BUNDLE  SACKS. 


How  TO  BUNDLE  SACKS. 


D 


GOOD  CONCRETE  175 


How  TO  SHIP  EMPTY  SACKS. 

Empty  sacks  are  valuable  property  and  should  be  handled  care-    How  to 
fully  at  all  times.     It  is  important  that  they  should  be,  made  up  into    s/iip  empty 
tight,  strong  bundles,  and  tagged  with  the  best  grade  of  linen  tags,    sacfc 
completely  filled  out,  so  that  each  bundle  in  the  shipment  may  be 
fully  identified.     All  railroads  recognize  the  importance  of  proper 
bundling  and  tagging  and  have  rules  providing  that  bundles  which 
are  not  properly  marked  and]  bound  shall  not  be  accepted  for  trans- 
portation.    The  instructions  given  below  are  based  on  the  railroads' 
rules  and  it  is  necessary  to  follow  them  for  this  reason,  as  well  as  for 
your  own  protection. 

BEFORE  BUNDLING  SACKS. 

Cull  out  all  sacks  that  have  been  wet  or  in  which  the  cloth  has    Do  not  ship 
become  weak  or  rotten.     They  are  not  worth  shipping.  rotten  or 

Cull  out  all  sacks  that  do  not  bear  the  brand  of  the  manufacturer  to    *°™  ° 
whom  you  are  shipping.     They  will  not  be  credited. 

Cull  out  all  sacks  that  show  signs  of  deliberate  misuse,  such  as 
sacks  that  have  been  cut  open  to  remove  the  cement  and  sacks  that 
have  been  soiled  by  using  them  to  carry  other  materials,  such  as  clay, 
lampblack,  dry  colors,  etc.  They  are  not  worth  paying  freight  on. 

How  TO  BUNDLE  SACKS. 

Lay  the  sacks  out  flat,  in  piles  of  50  each.  How  to 

Pass  a  wire  or  rope,  40  inches  long,  under  each  end  of  the  pile,          ^    ^ 
and  lay  a  third  wire  or  rope,  8'/2  feet  long,  lengthwise  on  top  of  the 
pile,  as  in  Figure  A.    Rope  must  be  at  least  3-16  of  an  inch  thick- 

Bring  the  two  short  wires  or  ropes  up  over  the  pile  of  sacks  and 
tie  them  tightly  as  in  Figure  B. 

This  will  roll  or  double  the  sacks  over  the  long  rope. 

Turn  the  bundle  over.  Bring  the  ends  of  the  long  rope  around  the 
ends  of  the  sacks.  Take  hitches  with  the  long  rope  around  the  two 
short  ropes  that  already  been  tied. 


176 GOOD  CONCRETE 

These  hitches  will  keep  the  short  ropes  from  being  slipped  over 
to  pull  any  sacks  out  of  the  bundle. 

Then  cross  the  long  rope  in  the  middle,  as  in  Figure  C,  bring  it 
around  the  middle  of  the  bundle  and  tie  tightly,  as  shown  in  Figure  D. 

This  will  make  a  bundle  that  will  stand  rough  handling.  It  will 
be  light  and  convenient  to  carry,  so  that  no  one  will  be  tempted  to 
drag  it.  If  the  ropes  are  tied  tightly  it  will  be  next  to  impossible 
to  pull  any  sacks  out  of  the  bundle. 

It  is  a  good  practice  to  put  one  of  your  business  cards,  letter  heads 
or  a  tag  with  your  name  on  it  inside  each  bundle,  as  this  will  enable 
the  consignee  to  identify  your  property  even  if  the  tag  should  happen 
to  be  detached. 

How  TO  TAG  BUNDLES. 

Tag  all        Use  nothing  but  linen  lags,  preferably  those  furnished  by  the  manu- 
bundles  facturer  to  whom  you  are  returning  the  sacks. 

Fill  out  all  the  blank  spaces  on  both  sides  of  every  tag. 

Fasten  the  tag  securely  to  the  bundle,  with  wire,  as  shown  in  Fig- 
ure C  or  Figure  D. 

How  TO  SHIP  SACKS. 

See  that  the  destination  on  the  bill  of  lading  is  an  exact  copy  of 
the  destination  shown  on  the  tags,  and  have  it  written  out  in  full. 
Do  not  allow  it  to  be  abbreviated  or  cut  short. 

Prepay  the  freight. 

Prepay  the        Be  sure  that  the  amount  of  freight  you  pay  is  shown  on  the  bill 
freight  on  of  lading. 

returned  sacks        0  ,         ,          ,  ,   .        , .        ,     , 

Send,  to  the  parly  to  whom  the  sacks  are  being  snipped,  me  orig- 
inal bill  of  lading  and  a  letter  saying  how  many  sacks  are  in  the 
shipment. 


GOOD  CONCRETE  1 77 

There  is  a  very  good  reason  for  every  suggestion  made  above, 
and  we  earnestly  recommend  that  you  tack  up  this  circular  where  it 
can  be  seen  by  the  people  who  handle  returned  sacks. 

Return  sacks  to  our  mill  at  Riverside  if  by  Southern  Pacific  Ry. 

Return  sacks  to  our  mill  at  Riverside  if  by  Santa  Fe  Ry. 

Return  sacks  to  our  mill  at  Crestmore  if  by  Salt  Lake  Ry. 

You  can  depend  upon  getting  a  square  deal  from  us  in  all  mat- 
ters pertaining  to  sacks,  but  to  follow  the  above  rules  simplifies  mat- 
ters enormously  and  saves  money  for  all  concerned. 

OUR  METHOD  OF  LOADING  CARS. 

We  weigh  each  empty  freight  car  to  obtain  the  correct  tare.     We  Correctness 
load  the  cement  into  the  car  direct  from  the  packing  room  under  a  of  our 
checking  system  which  gives  us  three  independent  tallies  upon  the  con-  weights 
tents  of  the  car.    When  the  loading  is  completed  a  tally  sheet  is  made 
and  fastened  to  the  inside  of  the  car  for  the  consignee's  convenience 
in  checking  the  out-turn  of  the  car.     The  car  is  then  weighed  with 
the  load,  which  must  verify  the  loading  tally,  or  the  car  is  not  al- 
lowed to  go  forward. 

We  operate  under  the  Trans-Continental  Weighing  &  Inspection 
Bureau  Agreement  No.  30,  and  our  weights  are  obtained  by  sworn 
weighmasters.  All  chance  for  error  in  count  of  shipments  is  re- 
moved before  the  bill  of  lading  is  issued. 

UNLOADING. 

We  attach  a  Red  Sticker  to  each  bill  of  lading  to  furnish  con- 
signees with  instructions  as  to  the  proper  method  to  follow  upon 
arrival  of  shipments  at  destination.  A  copy  of  this  notice  follows: 

"Please  check  the  contents  of  this  car  with  the  LOAD- 
ING CARD  which  is  tacked  inside  the  car.  The  contents 
have  been  checked  by  us  and  weighed  by  a  sworn  weigh- 
master.  Get  the  RAILROAD  AGENT  to  acknowledge 
any  shortage  by  a  notation  on  the  FREIGHT  BILL.  No 
claim  for  a  shortage  can  possibly  be  entertained  unless  both 


1_78 GOOD  CONCRETE 

the  FREIGHT  BILL  and  the  LOADING  CARD  are 
sent  us  bearing  the  proper  notations  made  by  the  RAIL- 
ROAD AGENT.  When  there  is  no  agent  at  the  destina- 
tion, any  variation  from  our  loading  must  be  verified  by  two 
responsible  parties,  and  a  record  made  of  the  condition  of 
the  seals  on  the  car." 

PAYMENT  OF  FREIGHT. 

We  sell  cement  f.  o.  b.  cars  at  destination  conditionally  upon  con- 
signees paying  the  freight  charges  and  deducting  the  amount  from  in- 
voice value  of  the  shipment.  We  prepay  freight  charges  to  prepay 
or  non-agency  stations  only,  and  immediately  render  cash  bills  to 
consignees  for  freight  charges  thus  advanced. 

CAR  SHORTAGES. 

In  periods  of  car  shortage  we  attach  another  "Sticker"  to  bills  of 
lading,  which  reads  as  follows: 

PONT  DELAY!     DO  IT  NOW!     UNLOAD  THIS  CAR! 

CARS  ARE  SCARCE  AND  GETTING  SCARCER.  OUR 
ABILITY  TO  FURNISH  CEMENT  IS  REGULATED  BY 
THE  RAILROAD'S  ABILITY  TO  FURNISH  CARS. 

ORDER  LARGE  CARS  AND  UNLOAD  PROMPTLY 

GENERAL  INFORMATION. 

Our  plant  is  located  at  Crestmore,  Cal.,  on  the  line  of  the  Crescent 
City  Railway  Company,  having  direct  connection  with  the  Southern 
Pacific.  A.,  T.  &  S.  F.,  and  S.  P.,  L.  A.  &  S.  L.  lines.  We  can 
make  delivery  to  all  points  via  these  lines  or  their  connections. 

Our  office  is  at  640  Title  Insurance  Building,  in  the  City  of  Los 
Angeles.  Our  telephone  number  on  the  Sunset  is  Main  5753  and 
on  the  Home  is  10527.  A  Private  Exchange  will  connect  you 
with  all  -ity  warehouses  as  well  as  with  office  departments. 


GOOD  CONCRETE  179 

APPENDIX. 
I.     OTHER  PUBLICATIONS. 

In  addition  to  "Good  Concrete,"  the  Riverside  Portland  Cement 
Company  issues  printed  matter  upon  special  subjects  which  it  will 
cheerfully  furnish  to  applicants  at  its  office  on  the  Sixth  Floor  of  the 
Title  Insurance  Building,  Los  Angeles.  Selections  can  be  made  from 
the  following  list: 

Bulletin  No.      1.      Concrete  Building  Blocks. 

Bulletin  No.    10.      Concrete  Surface  Finish. 

Bulletin  No.    18.      Reinforced  Concrete  Chimneys. 

Bulletin  No.  19.  The  Use  of  Cement  in  Sewer  Pipe 
and  Drain  Tile  Construction. 

Bulletin  No.  20.  Mixing  and  Placing  Concrete  by 
Hand. 

Bulletin   No.   21.      Concrete  Silos. 

Bulletin  No.   22.      Cement  Stucco. 

Bulletin  No.  23.     Concrete  Tanks. 

Bulletin  No.   25.      Concrete   Poles. 

Bulletin  No.   26.      Concrete  in  the  Country. 

Bulletin  No.  27.  Concrete  School  Houses  vs.  Fire 
Traps. 

Standard  Specifications   for  Portland  Cement  Sidewalks. 

Standard  Specifications  for  Cement  Hollow  Building 
Blocks. 

Standard  Building  Regulations  for  the  Use  of  Rein- 
forced Concrete. 

Standard  Specifications  for  Concrete  Road  and  Street 
Pavements. 

Standard  Specifications  for  Portland  Cement  Curb  and 
Gutter. 

Standard  Methods  of  Testing  and  Specifications  for 
Cement. 


INDEX 


Adobe 

As  Sub-base  for  Sidewalk  75 

Aggregate 

Definition    '- 1  7 

For   Sidewalks    84 

For  Curb  and  Gutter t  02 

For  Roads    119 

In  Concrete  Law  41-42 

Materials  for  1 8-20 

American  Society  of  Civil  Engineers 

Standard  Methods  for  Testing  Cement 130 

American  Society  for  Testing  Materials 

Specifications  for  Portland  Cement 11-102-138 

Asphaltic  Oil  Wearing  Surface I  32- 1  42- 1  46 

(See  Wearing  Surface.) 
Asphalt  Roads 

Cause  of  Destruction  1  12 

Concrete  for  Rigid  Foundation 112 

(See  Road  and  Pavements) 

Axioms Concrete     8 

Basalt    as    Aggregate—-  18 

Beaver  Board  ...  80-82-102 

Behavior  of   Concrete   towards  Metals 60-61 

Bituminous  Wearing  Surface 1  13 

Boiling  Test  for  Cement---  14 

Bonding    Concrete    52 

Briquette 

Tensile     Strength    ...  12-131 

Cars,  Methods  of  Loading  177 

Methods  of  Unloading  -  177 

Shortage  —  178 

Cement 

Asphaltic    ..  143 

Cement  Paste  34 

Covering   for    Protection 95 


182  INDEX 


Expansion  and  Shrinkage  in —  34-79-101 

Effect  of  Sea  Water  on  ...    62 

Rules   for  Use  of - 8 

Test  Pats  of .-131 

Chemical   Influences   59-60 

Coloring  Cement  92 

Concrete 

Consistency    .-45-58-105 

Definition    17-48 

Effect  of  Weather  53-54 

Mixing   -  -.48-51-105 

Proportioning   3 7-42-85-1  04 

Strength   53 

Size  of  Rock  ...  -    19 

Concrete 

Bonding  of  Old  and  New  52 

Depositing    -  —51-52-89-105 

Frozen    54 

Hardening  -  —53-54 

Tamping     51 

Concrete 

Crazing     56 

Effect  of  Alkali  and  Sea  Water  on  -  —64-66 

Expansion  and  Shrinkage   of—  54-79-101-115 

For    Sidewalks    73 

Resistance  to  Chemical  Influences  59-60 

Concrete  Axioms  8 

Concrete  Construction  8 

Concrete  Law  —26-37-40-42 

Application  44-47 

Considiere  and  Shumann   -  -  ..    55 

Consistency  (see  Mortar). 

Construction  of  Curb  and  Cutter  104 

Cracks 

In  Sidewalks  79-80 

Crazing    56 

Crown  for  Concrete  Roads  I  18 

Curbs  and   Gutters  101-108 

Construction   of   1 04 

Dimensions  103 


INDEX  ,83 


Expansion  and  Shrinkage  |  Q  \ 

forma  jQ3 

Proportions  of   Concrete —         j  Q4 

Specifications    ..  102-104 

Sub-grade      j  Q2 

Wearing   Surface    |  Q6 

Cyclopean  Concrete  |  9 

Depositing    (see  Placing). 
Drainage 

Of  Sidewalks   78 

Draw    Cracks    --  55 

Expansion  Joints  1  1  7-1  29 

Expansion  of  Cement  54 

In  Concrete  Road  Beds  1  15 

In  Curbs  and  Gutters  101 

In  Sidewalks  79 

Fills 

As   Foundation    for   Sidewalks    78 

As  Foundation  for  Gutters  103 

Floors  Laid  on  Hardened   Concrete   Base 93 

Forms    for    Concrete 

For  Cement  Sidewalks  89 

For  Gutter  and  Curb  103 

For  Roads  ...  -.130-137 

Treatment   of   5 1 

Foundation 

For  Concrete  Roads  127 

For  Sidewalks  --73-78 

Fuller,  Mr.  W.  B 40 

Grade  for  Gutter  102 

Grading   for  Concrete  Roads   126 

Granite  as  Aggregate  ---  18 

Gravel 

As   Aggregate    —20-85 

Gravel  Pits  21 

Hardened  Concrete 

Behavior  toward  Metals  ...  60 

Mineral  Oils  60 

Resistance  to  Chemicals  — 

Resistance  to  Sea  Water  61-62 


184  INDEX 


Sewage   ; 60 

Vegetable  Oils  60 

Hardening  of  Cement  14-1  5 

Irrigation  Pipe  I  52 

Laitance  ...     1  5-46-52 

Limestone  as  Aggregate  18 

Screenings    84 

Laying  Cement  Pipe  ----156 

L.  A.  County  Highway  Commission  ....114 

Macadam    (see   Road  and   Pavements). 

(See   Asphalt.) 

Machine  Concrete  Mixers  —  .---50-51 

Magnesia  in  Portland  Cement  ...  -•    12 

Marking  of  Sidewalks  80 

Measurements  of  Density  ---  -    57 

Mechanical  Analysis  --25-44 

Mechanical   Analysis  Curve   ..  26-30 

Michaelis,    Sr 14-15 

Miner's   Inch   -  -    -159-162 

Mixing    Concrete    --    48 

By    Hand    -    49 

For  Irrigation  Pipe  155 

For  Roads  120-127 

For  Sidewalks  -  1 87 

Machine  Mixing  50 

Mortar 

Color    92-106 

Consisting  of   45-87-155 

Density    of    34 

Expansion  and  Shrinkage  in  ---  -.--54-79-101 

Mixing    87-106 

Proportioning  for  Curb  and  Cutter  -••  ----106 

Proportioning  for  Sidewalk   86 

Strength  due  to  Sand  25 

Oil,  Asphaltic 

As  Wearing  Surface  of  Roads  : 132-140 

Specifications    --  ---133 

Solubility    1 134 

Test  for  Asphalt  ...  ....135 

Temperature     135 


INDEX  185 


Parting  Strips  for  Sidewalks  82 

Pipe,   Cement  for  Irrigation 

Advantages    of    |  5  1 

Curing    156 

Laying    1  56 

Specifications    153 

Valves     157 

Pipe,   Cement   for  Sewer 

Consistency     - |  66 

In  Europe  1 66 

Machine  Made   167 

Specifications    1 65 

Placing  Concrete  and  Mortar   58 

For  Curbs  and  Gutters  105-106 

For   Roads    1 2  1 

For  Sidewalks  89 

Road  Foundation  121-128-139 

Portland  Cement 

Application   of   --  7 

Definition    1  1 

For  Concrete  Roada   130- 138 

Hardening    14 

Neat    --    12 

Specific  Gravity 12 

Standard    Specifications    - 

Setting  Time  -  -.13-130 

Strength   14 

Proportioning  Concrete 

By   Voids   35 

By    Trial    --39-40 

Concrete  Law  40-42 

For  Curbs  and  Gutters  104 

For    Roadbeds    —119-127-138 

For   Sidewalks    87 

Methods  of   ..  37-42 

Protection   of   Concrete 

For  Roads   121 

For  Sidewalks  ... 

General  Rules  for  9 


186  INDEX 


Riverside   Portland   Cement   1  02 

General    Information    1  78 

Publications    I  79 

Roads  and  Pavement,    Concrete 

Advantages    of    113-114 

Bituminous  Wearing  Surface  1  13 

Crown     I  |  8 

Expansion  and  Shrinkage  1  15-117 

One  Course  and  Two  Course  113 

Quality  of  Concrete  Necessary  for  114 

Specifications  for  1  |  5 

Wear  of  Roads  M4 

Roads  and  Pavements,   Concrete  117 

Aggregate    -  -.119-131-132 

Expansion    Joints    I  17 

Mixing   Concrete   120-127-139 

Proportions   for    -  118-177-138 

Protection  after  Placing  121-140 

Roads  and  Pavements,   Concrete 

Asphaltic   Oil  Wearing  Surface   Specifications   125-132-142 

Forms   130-137 

Foundation   127 

Grading     126-137 

Placing   -                                                                                          -.121-128-139-146 
Proportions   -  127-138 

Rock 

Difference  between  Rock  and  Sand I  7 

Effect  of  Size  upon  Strength  of  Concrete —  --    19 

Voids  ...  3 1  -33-38 

(See  Mortar.) 

For    Curbs    1 02 

For  Roads  132-138 

For    Sidewalks    84 

General    Character    I  8-20 

Sacks 

Advantages  of  Cloth  - 1  72-1  74 

Return  of  Empty  174-177 

Value  of  1  7 1 

Sand 

Asphalt   Wearing  Surface   1 45 


INDEX  187 


Description  of  2  1  -2'6 

For    Curbs    1 02 

For  Roads  131-138 

For  Sidewalk  84-85 

General    Character    2 1  -25 

Irrigation  Pipe   1  53 

In  Asphalt   1  42 

Testing  of   (see  Aggregate)    8 

Specifications    (see    Mortar)     46 

Voids     -  31-33 

Sandstone    as    Aggregate 18 

Schutte,    A.    E 40 

Screenings,   Rock 

For   Asphaltic  Wearing  Coat  of  Roads 133 

For  Sidewalks    84 

Used   as   Sand 30-31 

Sea  Water 

Effect   on   Concrete 6 1  -64-66 

Remedies 62 

Setting  of  Cement 

Time  of  13-130 

Shrinkage  of  Cement 34 

In   Concrete   Road   Beds 115-117 

In   Curbs  and  Gutters -—101 

In  Sidewalks 79 

Sidewalks,   Cement   ...  —73-98 

Advantages   of    73 

Adobe    Foundations    75 

Air  Bubbles  -    94 

Cause  of  Defects  ...  97-98 

Coloring  

Consistency  of  Concrete  for— - 

Covering   for   93-94-95 

Drainage   of   78 

Dusting  of 

Finishing   of   92 

Foundations    for    -  73-78 

Guide  Strips  

Marking  of  80-93-94 

On   Fills  78 


188  INDEX 


Parting  Strips  ---  ...    82 

Placing  Concrete   and   Mortar 89 

Placing  91 

Preparation  of  Concrete  and  Mortar----  ... -82-86 

Proportions    for    87 

Prevention   of   Cracks  in --    79 

Wearing  Coat  86-87 

Sieves  2*5 

Standard  Mesh  1 3  1 

Sizing  of  Particles  of  Sand 23-24 

Specifications  for  Concrete  Roads  (with  Asphaltic  Wearing  Surface) 

City  of  Glendora 1 25 

L.   A.    Highway   Com -137 

Specifications   for   Curb  and  Gutter 102-104 

Specifications   for   Portland    Cement    1  I 

Specifications  for  Sidewalks    73-98 

Specifications   for   Street  Paving,   in   City  of  Los  Angeles —  --..142 

State  Highway  Commission I  1 4 

Sulphuric  Anhydride   in   Portland   Cement -.    12 

Tables 

I.  Showing    Relation    between    Diameters    and    Total    Surface    Areas    in 

One    Cubic   Yard    of   Material 24 

Tables 

II.  Tests  Showing  Effect  of  Size  of  Grain  on  Strength  of  Mortar 25 

III.  Table  of  Sieves  and  their  Meshes 25 

Tables 

IV.  Tests   Showing   Relation    of   Mechanical    Analyses   and   Strength    of 
Mortar    27 

V.  Table  of  Specific  Gravities  and  Weight  of  One  Cubic  Foot  Solid--.    32 
Table   VI. 

Voids  for  Different  Weights  per  Cubic  Foot * 33 

Table   VII. 

Amount  of  Plastic  Mortar  from  One  Sack  of  Cement 35 

Table   VIII. 

Table  Showing  the  Sizes  Necessary  to  Produce  Densest  Concrete —        --    43 
Table    IX. 

Compressive    Strength    of    Average    Concrete    Made    at    U.    S.    Arsenal, 

Watertown,    N.    Y 54 

Table   X. 

Showing  Normal  Changes  in  Volume,  Inches  per   100  Feet  of  Length 55 


INDEX  189 


Table   XII. 

Weights  per  Cubic  Yards  of  Different  Aggregates 67 

Table   XIII. 

Percent  of  Shrinkage  in  Rock  and  Screenings  68 

Table  XIV. 

Table  of  Quantities  for  One  Cubic  Yard  of  Concrete  Rammed  in  Place-—    69 

Table  XV. 

Sidewalks — Quantities   for   Base 88 

Sidewalks — Quantities   for  Top  88 

Table   XVI. 

Weight  of  Coloring  Matter  per  Sack  of  Cement 90 

Table  XVII. 

Barrels  of  Oil  per  100  Feet  of  Roadway,  Cubic  Yards  Screenings 122 

Quantities   of   Concrete    1 22 

Table   of  Proportions 

For  Cement  Irrigation  Pipe I  62 

Table   XVIII. 

Amount  of  Water  Flowing  Through  Cement  Pipe  Running  Full  161 

Tamping  Concrete  5 1 

Trap   as   Aggregate 1 8 

Screenings   84 

Temperature 

Expansion    and    Contraction    from I  01-116 

Effect  on  Strength  of  Concrete 54 

Of  Oil  in  Asphaltic  Surface .—  135 

Voids  in  Sand  Rock 

Determination  of  Per  Cent. 3  1  -33 

For   Proportioning   Concrete   38 

Volumetric  Synthetic   Method 40-5  7- 1  20 

Warren   Bros.    Construction   Co 40 

Water 

Chemical  Composition  of  10Z 

Effect  of  Chemical  Composition  on  Strength  of  Concrete-—  —47-48 

For   Concrete    Roads    --  — -130 

For   Irrigation    Pipe    -- 

Methods  of  Mixing 49 

Proportion  for  Concrete  —  8-45-47 

Units    of    Measurement    for 

Water  Tightness  of  Concrete 

Depending  on  Density  57 


190  INDEX 


For  Sewer  Pipe 1  66 

Waterproofing   Compounds    58 

Wearing  Surface 

Curbs  and  Gutters 1  06 

Roads   132 

Sidewalks    86 

Weather 

Effect  on  Hardening  of  Concrete --    53 

Weir    Table    1  63 


TA  Good  concrete:   a  manual.... 

681  UNIVERSITY  OF  CALIFORNIA  LIBRARY 

r}^9  Los  Angeles 

This  book  is  DUE  on  the  last  date  stamped  below. 


JUL1 


Form  L9-30m-ll,'58(.8268s4)444 


/aK&&jm 


